The contents of chlorophyll,soluble sugars,soluble proteins and thiobarbituric acid reaction substance(TBARS),chlorophyll fluorescence parameters,net photosynthetic rate as well as the activities of superoxide dismutase(SOD)and peroxidase(POD)of flag leaves at the late growth stages were studied by using C Liangyou series of hybrid rice combinitions as material and Shanyou 63 as control.The C Liangyou series of hybrid rice combinations used in the experiment included C Liangyou 396,C Liangyou 87,C Liangyou 755 and C Liangyou 34,which all used C815S as male sterile line.The contents of chlorophyll,soluble sugars and soluble proteins in flag leaves of the C Liangyou series combinations at the late growth stages were higher than those of the control,whereas the TBARS content was lower than that of the control.The activities of SOD and POD were significantly higher than those of the control on the 7th day after heading,and then decreased slowly.ΦPSIIvalue and qP value of flag leaves decreased at the late growth stages,and these two parameters in flag leaves of the C Liangyou series combinations were higher than those of the control,while the qN value increased at the late growth stages and was lower than that of the control.The net photosynthetic rate of flag leaves at the late growth stage was higher compared with the control.These results suggest that slow senescence and strong photosynthetic capability in flag leaves at the late growth stages are the physiological basis of the C Liangyou series combinations. The contents of chlorophyll, soluble sugars, soluble proteins and thiobarbituric acid reaction substance (TBARS), chlorophyll fluorescence parameters, net photosynthetic rate as well as the activities of superoxide dismutase (SOD) and peroxidase (POD) of flag leaves at the late growth stages were studied by using C Liangyou series of hybrid rice combinitions as material and Shanyou 63 as control. C Liangyou series of hybrid rice combinations used in the experiment included C Liangyou 396, C Liangyou 87, C Liangyou 755 and C Liangyou 34, which all used C815S as male sterile line.The contents of chlorophyll, soluble sugars and soluble proteins in flag leaves of the C Liangyou series combinations at the late growth stages were higher than those of the control, while the TBARS content was lower than that of the control The activities of SOD and POD were significantly higher than those of the control on the 7th day after heading, and then decreased slowly. ΦPSIIvalue and qP value of flag leaves decre decrement ased at the late growth stages, and these two parameters in flag leaves of the C Liangyou series combinations were higher than those of the control, while the qN value increased at the late growth stages and was lower than that of the control. net photosynthetic rate of flag leaves at the late growth stage was higher compared with the control. These results suggest that slow senescence and strong photosynthetic capability in flag leaves at the late growth stages are the physiological basis of the C Liangyou series combinations.