Abstract: Abscisic acid(ABA) and 6-benzylaminopurine (6-BA) were used to investigate their effects on activities of key enzymes in carbon assimilation in maize seedlings under water stress. The experiment was conducted with pot-cultural maize seedlings at stage with 3 leaves. 105mol/L ABA and 6-BA were sprayed on leaves at the beginning of soil drought. The results showed ribulose-1, 5-bisphosphate carboxylase (RuBPC) activity was slightly higher at the early stage of water stress and then decreased rapidly. while phosphoenolpyruvate carboxylase(PEPC) and pyruvate phosphate diklnase(PPDK) activities lowered with the increasing water stress. Abscisic acid(ABA) of 10-5mol/L inhibited the RuBPC activity considerably and affected the activities of PEPC and PPDK. 10-5mol/L 6-benzylaminopurine(6-BA) enhanced RuBPC. PEPC and PPDK activities markedly in maize seedlings under water stress. It is clear that the activities of these enzymes are increased by ABA and 6-BA. and the effects of ABA and 6-BA inhibited markedly by CHX, while these enzymes activities can not be stimulated directly by external application of ABA, 6-BA and CHX. The inhibition of CHX to the effect of ABA and 6-BA indicatid the relationship between the increased synthesis of enzyme protein and hormones regulation. The changes in water potential. contents of chlorophyll, stomatal resistance and photosynthetic rate as well as the changes above-mentioned criteria after the treatmentns of ABA and 6-BA in maize seedlings under water stress were studied.The results possibly support a hypothesis of ABA and 6-BA induced brought resistance in maize seedlings. But the basic biochemical mechanisms of ABA are different from that of 6-BA.