Jae-chang was born 1866 (Daegu Seo Clan) in Bosong in South Jeolla Province.
He was the fourth son of Seo Gwang-ho, governor of Dongbok County and Lady Lee of Seongju.
He studied in Japan, recommended by Yu Dae-chi and Lee Dong-in.
He entered a Toyama military school with Jae-pil, but in July he went to Seoul to plan a revolt with Kim Ok-kyun, Park Yeong-hyo and other members of Reformist Partys, Hong Yeong-sik, Park Yeong-kyo, Yun Chi-ho, Yun Ung-ryeol, Jae-pil and his father's fifth cousin Soh Kwang-pom.
Queen Min mobilized Qing dynasty forces, who killed Hong Young-sik and Park Yeong-kyo in battle.