Although heavy metals are highly toxic to many plants, a number of plant species growing on metalliferous soils accumulate heavy metals to extraordinary levels in their tissue without showing toxic symptom. These plants are termed as hyperaccumulators, which have important value to study evolutionary, biochemistry and physiological aspects involved in the metal uptake process. Plant photosynthesis is sensitive to heavy metal stress. Nevertheless, there are only few reports of hyperaccumulators Photosynthesis under heavy metal stress. In the present study, the relationship between photosynthetic performance and Cd concentration in Viola baoshanensis and V. yedoensis was compared in the laboratory by imaging-PAM. Field survey indicated that Cd concentrations in shoots of V. baoshanensis and V. yedoensis were 867 mg/kg and 2 mg/kg, respectively. Cd accumulation factor and translocation factor in V. baoshanensis were larger than 1, while in V. yedoensis were less than 1. The results indicate the former species is a Cd hyperaccumulator, whereas the latter is not. A number of photosynthetic indexes (F_m, I_k, P_m) of V. baoshanensis were significant lower than those of V. yedoensis, but other indexes (F_o, F_v/F_m and () did not differ significantly between the two species. For V. yedoensis, there was no significant correlation between Cd concentrations in shoots and photosynthetic indexes. For V. baoshanensis, there was a significant negative correlation between F_m, P_m and I_k and Cd concentrations. The F_v/F_m of the two species was approximately 0.8, indicating there was no Cd damage on photosynthesis. However, the low Fm in V. baoshanensis indicates a negative effect of Cd on the electron transport, and/or the functioning of the chlorophyll pigments; and the low Pm and Ik in V. baoshanensis indicate Cd decreased the light tolerance and electron transport. The two species both had a high α level, indicating the normal functioning of the light absorbing system under Cd stress. Overall, the results suggest that the electron transport system of V. baoshanensis is less efficient under Cd stress.