Abstract: The experiment was conducted to study the mechanism of drought tolerance in C₄- phosphoenolpyruvate carboxylase(PEPC) gene(C₄-PEPC) transgenic rice(PC), PC and its untransformed wild-type rice lines, Kitaake(WT) as materials. Pretreated by light(light intensity:600 μmol·m^-2·s^-1) and dark on two rice lines with 4 leaves for 24 h, the pretreated rice lines were then conducted by 15% polyethylene glycol-6000(PEG-6000) simulated drought stress conditions for 4 h. Two inhibitors(one for Abscisic acid:100 μmol·L^-1 nordihydroguaiaretic acid(NDGA) and the other for hexokinase(HXK):10 mmol·L^-1 glucosamine(Gluc) were also added by root during the PEG-6000 treatment. Compared with WT rice lines, there were higher relative water content, lower malondialdehyde content and pro content in PC rice lines after drought treatment for 4 h involved in ABA and HXK pathways, conferring drought tolerance. But pre-dark treatment reduced the advantage of PC for drought tolerance. Soluble sugar content in two rice lines were increased in pre-light treatment and decreased in pre-dark treatment, which were regulated by ABA and HXK pathway. Among them, the Gluc inhibition of soluble sugar content in PC pre-light treated was the largest after the PEG treatment. There was no difference in soluble protein content of two rice lines either pretreated by light and dark during the PEG treatment. Similarly, pre-dark treatment reversed or eliminated the changes in two rice lines, which trends changed synchronously as those of sucrose, glucose and fructose contents. PEPC activities in PC lines did not change by pre-light or pre-dark treatments, showed PC belongs to constitutive expression. ABA and HXK pathways regulated negatively PEPC activity, which was synchronous with its low level of glucose in PC lines. Therefore, PC rice lines alleviated the damages of drought stress by sugar involved in ABA and HXK pathways, exhibiting stable photosynthetic ability and drought tolerance.