Abstract: This study analyzed the relationship between lightning activity and cloud microphysics within two isolated thunderstorm cells over southern China on 13 and 20 Jun 2016. Furtherly, the probable physical processes that affected the lightning activity were explored. The observations were provided from the S-band polarimetric radar, lightning-detection system and the sounding data. The results show that (1) there is a lag relationship between lightning activity and the changes in horizontal reflectivity (ZH) intensity and supercooled liquid water content of mixed-phase region. It can be used for early warning of lightning activity. (2) Before lightning activity occurring, an increase in positive values of differential reflectivity (ZDR) facilitates the lightning activity, specifically, large ZDR values in mixed-phase region; however, this relationship is weak during the second stage of lightning activity. (3) The variation of graupel content suggests the mechanism of riming electrification dominates the electrical process during the early lightning activity; however, the leading role will disappear during the later lighting activity. This study is expected to deepen our understanding of the cloud microphysics relating to lightning activity within isolated thunderstorms.