The secret society Yeyongsokhoe, led by Pastor Kim Hui-un of Yesan Church, was formed by students of Yesan Public Agricultural School and operated from June 1939 to December 1941. Lee Min-gu took part alongside fellow members Im Hyeong-seon, Yun Yeong-won, Choi Gyeong-yong, Jang Jun-hwan, Kim Dong-sik, An Se-yeong and Park Dae-yeong in pursuit of Korean independence.