Jong-Han Leem got an MD at Yonsei University in 1987, and got PhD degree at Yonsei University in 1997, and was a visiting scholar at CDC, USA in 2003-2004.

He was former Chairman, Korean Society of Environmental Health & Toxicology(2018-2019) and is a chairman Korean Academy of Primary Health Care (2019- ).

His major research area is air pollution epidemiology. His doctoral thesis was on the adverse health effect of air pollution. He first time applied time series model in air pollution study in South Korea. He has involved the health risk assessment and management of air pollution in Seoul metropolitan area. He also first time reported the clinical case for Agent Orange in South, and his many studies reported inhalation and systemic toxicities of humidifier disinfectants in South Korea.