In China, science educators as a professional group were originally referred to as academic staff responsible for teaching the subject-based science teaching methods course at the related science departments at teachers' universities. In this study, a biographic method was used to approach the professional life of Zhixin Liu, who was a senior science educator at the Department of Chemistry at Beijing Normal University, to reveal how he has become a professional science educator and what influences he has brought about to the chemistry education community over the past half a century in China. The main findings of this study were the two roles played by Liu in the enterprise of chemistry education in China: as an agent to disseminate national curriculum policies and as a scholar to construct the Chinese theories of chemistry teaching. Results show that the two roles were intertwined during the whole professional life of Liu. The implications of Liu's life story for dealing with the relationships between policy and practice and between theory and practice in the field of science education are discussed.