Abstract:This paper studied the effects of weak light on the photosynthetic characteristics, assimilates allocation, yield formation, and seedling growth of different ecotype capsicum (hot pepper and sweet pepper). The results showed that under weak light, the net photosynthetic rate (Pn), dark respiration rate (Rd) , night respiration rate (Rn), transpiration rate (Tr), water use efficiency (WUE), light compensation point (LCP), CO2 compensation point (CCP) and carboxylation efficiency (CE) of test capsicums decreased, while their apparent quantum yield (AQY) increased. The decrease of Pn was considered as a result of non-stomata restriction. Weak light increased plant height/stem diameter ratio and specific leaf area, but decreased root/shoot ratio, total dry mass, and seedling’s healthy index. Under the effect of weak light, the formation of biological and economic yields was inhibited significantly, and the allocation of assimilates to stem and leaf was increased while that to fruit decreased. Hot pepper under weak light had lower light compensation point, higher relative healthy index, higher relative yield per plant, and higher relative setting rate, showing a stronger capability of weak light tolerance than sweet pepper.