Abstract: Two Italian Ryegrass varieties (‘Maximus' and‘Hercules') were studied with pot-culture experiment in physiological and biochemical responses against waterlogging.The results showed that:with mild stress of waterlogging (water just covering soil) , the proline content of ‘Maximus' and ‘Hercules' was increased by225.6% and 509.7%, respectively, compared with control group although other compound indices observed no significant differences (P >0.05) .Under severe waterlogging (submerged soil for 4cm) , the significant physiochemical changes were observed while compared with control group (P<0.05) in the chlorophyll content in leaves of ‘Maximus' and ‘Hercules' decreased about 23.5% and 63.5%, respectively;the proline content of‘Maximus' and‘Hercules' increased by 405.9%and 513.8%, and the MDA content of both varieties increased by48.9%and 76.2%, respectively;the peroxidase activity of‘Maximus' and ‘Hercules' was increased by 204.0%and 74.1%, respectively, while superoxide dismutase and catalase activity were increased first and then decreased.With water slight covering, there was no significant change in plant physiology observed until the 7th day of waterlogging, while by deepwater submergence, the physiochemical responses started at the 4th day of treatment.The results suggested that the ryegrass could grow normally for 7days under the mild submergence but only for 4days whenever submerged with deepwater.