 In January 1998, joining a French club Strasbourg, Seo became the first South Korean player who played in the Ligue 1.He successfully spent his first season by contributing to their survival in the Ligue 1, but he was pushed to the bench next season after his manager was replaced.He participated in the 1998 FIFA World Cup although he got chickenpox, transferred from his son, but showed unnoticeable performance with the team's elimination in the group stage.