After liberation of Korea in 1945, he participated in the founding of the Korean Pediatric Science Society in September.
From January 1946, when the movement against trusteeship became a social controversy, university professors decided not to intervene in political affairs, led by Yoon Il-sun at the time, but Lee Byung-nam became a civilian health expert on the left wing.
[3] While serving as a professor of Pediatrics at Seoul National University College of Medicine, he was dismissed for participating in the leftist struggle in 1947, and was reopened in Jongno.
In August of that year, he was elected as deputy to the Supreme People's Assembly, and on September 9, after the Democratic People's Republic of Korea was formally established, he was appointed as its first Minister of Public Health in the Cabinet of North Korea led by Premier Kim Il Sung.
[4] In 1955, he became the Health Minister of North Korea again and was appointed chairman of the Central Committee of the Korean Red Cross that year.