Frontal heavy rainfall (FR) and coastal warm-sector heavy rainfall (WR) are two typical types of precipitation in South China during the pre-summer rainy season. FR and WR are found to be generated by different mechanisms, but their differences in microphysical features and relevant possible reasons are not well understood. In the present study, dual-polarization observations merged from ten radars are utilized to investigate microphysical characteristics of two coexisting convective systems producing FR and WR. Overall, the WR has a stronger convection intensity, larger raindrop size, and higher liquid water content than the FR. The larger raindrops might be partly attributed to deeper warm-sector convection with potentially more active ice-related processes. Interestingly, raindrops in the WR are still larger even when the WR has similar convection intensity with the FR, which can be possibly explained by active warm rain processes with higher low-level humidity and more evident low-level rotation in the WR. In addition, the FR was originally developed near the front and then vacated from the front into the warm sector, which exhibits obvious temporal evolution in microphysical characteristics. Despite weaker convection intensity, the FR away from the front manifests a larger raindrop size than the FR near the front possibly because of more abundant environmental moisture in the warm sector.