Abstract: Effects of salt stress on photosynthetic characteristics and chlorophyll content of Sapium sebiferum seedlings was studied. The results showed that the change of net photosynthetic rate (Pn) of Sapium sebiferum seedlings from various provenances was different. The Pn of GC2 provenance showed the tendency of increased first and then decreased. The change of the rest provenances was gradually descending with increasing of salt stress. Compared with control the stomatal conductance（Gs）of both XN1and GC2 provenances increased under 020 %NaCl stress, Gs of the rest provenances decreased. According to the change ranges, they were ordered as HS1>HZ2>GCH1>SC4. The Gs of whole provenances was lower than that of the control under 040 %,060 % NaCl stress. The intercellular CO2 concentration（Ci）of different provenances showed a distinct tendency. The chlorophyll content (Chl)of GC2,GCH1 and HZ2 provenances was gradually descending with increasing of salt stress, but provenances of XN1,SC4 and HS1 showed irregular changes. Correlation analysis showed that Pn was significantly positively correlated to Gs, Ci，Tr(p＜001),but correlation between Pn and Chl was not obvious. By combining the changing ranges of Pn and Chl, we drew a conclusion that both XN1 and GC2 provenance showed stronger tolerance under lower salt stress, SC4 and GCH1 took the second place, whereas GC2 provenances could keep certain photosynthesis under middle salt stress, and its tolerance to salt stress was the strongest.