Abstract: Effects of drought were investigated on net photosynthetic rate(P_n,μmol/(m~2·s)),stomatal conductance(g_s,mmol/(m~2·s)),subcelluar CO_2 concentration(C_i,μmol/mol) and mesophyll conductance to CO_2(g_m,mol/(m~2·s)) in potted seedlings of four woody species(Quercus liaotungensis and Fraxinus rhynchophylla,Spiraea pubescens and Lepsedeza bicolor)from Q.liaotungensis forest in Beijing Dongling mountain.The results showed that soil drought which caused decreases in P_n,g_s,and g_m.C_i was maintained stable in two shrubs during the whole drought duration,whereas it was stable in two tree species only under mild drought but increased under serious drought.This suggests that the limitation to photosynthesis under drought conditions was not entirely attributed to stomatal limitation,but mainly to non-stomatal limitation.