Abstract: Chilling injury is one of major factors limiting the yield and quality of Rhododendron hybridum.The change in chlorophyll fluorescence kinetic parameters of four R. hybridum cultivars, i.e., ‘Wucai’,‘Fenhong’,‘Meihong’and ‘Puhong’ was studied under low temperature stress gradient (0℃, 3℃,5℃ and 10℃). The data obtained in this experiment showed that the maximum photochemical efficiency of PSⅡ (Fv/Fm), the actual photochemical efficiency of PSⅡ(Yield), and the photochemical quenching coefficient (qP) all decreased simultaneously under the low temperature stress, whereas the nonphotochemical quenching coefficient (qN) showed a rising trend. It was indicated by the values of chlorophyll fluorescence parameters of the four R. hybridum cultivars that ‘Puhong’ was most affected, followed by ‘Meihong’ and ‘Wucai’, and ‘Fenhong’ was the least affected by freezing. These results indicated that R. hybridum was very sensitive to low temperature stress that could damage the photosynthesis apparatus, resulting in reduction in the light energy absorption, efficiency of light energy conversion and photosynthetic electron transport efficiency.