In order to elucidate the role of ascorbate-glutathione (ASC-GSH) cycle to drought stress, the activities of antioxidant enzymes and the levels of molecules involved in the ASC-GSH metabolism were studied in Trifolium repens seedlings subjected to polyethylene glycol (PEG)-induced water deficit. Compared to the control, the contents of ascorbate (ASC), dehydroascorbate (DHA) and glutathione disulfide (GSSG) increased in PEG-treated seedlings, whereas the glutathione (GSH) content kept constant during the drought period. Further more, the values of ASC/DHA and GSH/GSSG ratios decreased in the presence of PEG. Except for that of monodehydroascorbate reductase (MDHAR), the activities of ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR) and glutathione reductase (GR) were upregulated during water deficit, and the increases of APX and DHAR activities were much higher than that of GR activity. These data indicated that fluctuations of the ASC-GSH metabolism resulted from PEG may have a positive effect on drought stress mitigation in T. repens, and the antioxidant protection in ASC-GSH cycle can be attributed mainly to ASC, APX and DHAR.