A young Korean layman executed at Seoul’s Small West Gate in 1866 during one of the most severe persecutions of Christians in Korean history.

Saint Alexius U Se-yong was a young Korean Catholic layman put to death in Seoul in 1866 during the sweeping persecution of Christians ordered by the regent Heungseon Daewongun. Born around 1845 in the Hwanghae region of what is now North Korea into a country where Catholicism had spread almost entirely through Korean lay initiative rather than foreign missionaries, Alexius grew up within the underground, illegal Catholic communities that had persisted despite recurring waves of state persecution stretching back to the late eighteenth century. In 1866, the Korean government launched a particularly brutal crackdown on Christians, executing thousands over the following years, and Alexius, still in his early twenties, was arrested, refused to renounce his faith, and was beheaded at Seoul’s Small West Gate execution ground on March 11, 1866. He is honored today as one of the 103 Martyrs of Korea, laypeople, priests, and a bishop canonized together in 1984 by Pope John Paul II during his historic visit to Seoul, the first canonization ceremony ever held outside Rome.

Quick Facts

• Born: circa 1845, in Seoheung, Hwanghae Province (present-day North Korea)
• Died: March 11, 1866, at the Small West Gate, Seoul, South Korea (martyred, age about 20)
• Feast Day: September 20 (with the Korean Martyrs)
• Beatified: October 6, 1968, by Pope Paul VI
• Canonized: May 6, 1984, in Seoul, South Korea, by Pope John Paul II
• Venerated as: one of the 103 Martyrs of Korea

Who Was Saint Alexius U Se-yong?

Alexius U Se-yong was born around 1845 in the Hwanghae region of northern Korea, into a Catholic community that existed entirely outside the protection or approval of the state. Korean Catholicism had a distinctive origin among the world’s mission churches: it began in the late eighteenth century not through the arrival of foreign missionaries but through Korean scholars who encountered Catholic texts brought back from China and converted on their own initiative, establishing a lay-led Church that persisted underground through repeated, sometimes ferocious waves of government persecution for decades before the first resident missionary priests ever arrived. Alexius grew up within this tradition of hidden, resilient lay faith. In 1866, the Korean regent Heungseon Daewongun, alarmed by foreign political pressure and internal fears of Christian influence, launched what became one of the largest and most severe anti-Christian persecutions in Korean history, resulting in thousands of executions over several years. Alexius, still a young man in his early twenties, was arrested as part of this crackdown, refused under interrogation to abandon his Catholic faith, and was condemned to death. He was beheaded at the Small West Gate execution grounds outside Seoul on March 11, 1866.

Historical Setting

Alexius’s death occurred during the persecution of 1866, triggered in part by the Daewongun’s suspicion of Catholicism as a foreign and politically destabilizing influence, compounded by tensions surrounding French and other Western intervention in East Asia during this period. Korean Catholics, numbering in the tens of thousands by the mid-nineteenth century despite the religion’s continued illegal status, had already endured several earlier waves of persecution dating back to 1801, and the 1866 crackdown proved to be the deadliest, claiming thousands of lives, including French missionary bishops and priests as well as a great many Korean laypeople like Alexius.

Why the Church Venerates Saint Alexius U Se-yong

The Church venerates Alexius as part of the extraordinary witness of the Korean Catholic Church, a community that took root and grew almost entirely through the courage of its own laypeople rather than through missionary importation, and that paid an immense price in blood across nearly a century of intermittent persecution before religious freedom was finally secured. His youth at the time of his martyrdom, and his membership among the many ordinary laypeople — rather than clergy or foreign missionaries — who make up the bulk of the 103 Korean Martyrs, highlights the depth of lay conviction that sustained Korean Catholicism through its most dangerous era.

Canonization and Feast Day

Alexius U Se-yong was beatified by Pope Paul VI on October 6, 1968, and canonized on May 6, 1984, by Pope John Paul II during a papal visit to Seoul, South Korea — a ceremony notable as the first canonization ever conducted outside Rome. He was canonized together with 102 other Korean martyrs, clergy and laity alike, whose deaths spanned the persecutions of the nineteenth century. The group’s shared feast day is September 20.

What Catholics Can Learn Today

Alexius’s brief life is a testimony to the strength of a faith that took root without the presence of clergy or institutional support, sustained instead by ordinary believers determined to hand faith on to one another under constant threat. For Catholics today, his example is a reminder that the Church’s endurance has often depended less on hierarchy and infrastructure than on the quiet, dangerous fidelity of individual families and young people willing to risk everything for what they believed, a pattern of lay courage that predates and outlasts whatever institutional support eventually arrives.

A Prayer to Saint Alexius U Se-yong

Saint Alexius U Se-yong, young martyr of Korea, who held to the faith your own people handed down to you at the cost of your life, pray for young Catholics today facing pressure to abandon what they believe. Give us the quiet courage of the Korean martyrs, who kept the faith alive in secret for generations without priests or protection. Strengthen the Church in Korea and in every place where believers still worship in danger, and help us treasure the faith we may take too easily for granted. Amen.

Sources

• Vatican.va, biography for the canonization of the 103 Martyrs of Korea (1984)
• the Catholic Church in Korea, official historical archive
• Encyclopaedia Britannica
• the Roman Martyrology