Abstract: The seasonal variations in chlorophyll content and chlorophyll fluorescence of twoyearold Castanopsis hystrix were investigated under 100%, 80%, 30% and 20% of full light intensity to study the adaptability of C. hystrix seedlings to light condition. The results showed that the chlorophyll fluorescence parameters Fo, Fm, Fv/Fm, Fv/Fo and φPS II measured under low light intensity (20%, 30% of the full light) were significantly higher than those corresponding values measured simultaneously under higher light intensity (fullexposure and 80% of the full light). The seasonal variation of Fo value under the same light intensity showed the similar change trend to the temperature variation in different seasons, i.e., the Fo value changed rapidly in January and February, but it changed gently in other months. The values of Fm, Fv/Fm and Fv/Fo parameters declined wavily during June, July and August, suggesting that the intense sunshine and high temperature laid somewhat negative effect on the photosynthesis of C. hystrix seedlings. The chlorophyll contents (chlorophyll a, chlorophyll b and total chlorophyll) were all increased under the shaded condition, which significantly differed from that of under the full light exposure condition (p<005), the highest cholorophyll contents were observed under 30% of the full light. The content of carotenoids was reduced with the decrease of light intensity at the initial stage, then it was increased gradually to the highest level under 20% of the full light (p<005 comparing with full exposure). It was concluded that the appropriate shading or growing C. hystrix seedlings understorey of the forest in Nanning area would be beneficial to the seedling growth and development.