Abstract:Intensities of photosynthesis of Chinese chestnut(Castanea mollissima Bl.)(trees and seedlings)were determined by colorimetric method under differend laboratory and field conditions,in the Shantung Pomology research institute. The treetments used were:foliar spray of essential elements to seedlings in sand culture experiments,and of some nutrient solution to mature trees;irrigation to roots or spray of water on leaves;Co2 fertilization by increasing Co2 concentration in the air,and application of certain growth hormones.Our results were,photosynthetic intensities of all the plants under treatments showed a higher rate than those of the controls.For example,photosynthetic rate of the seedlings in sand culture sprayed with 5% of P solution is 2.78 Co2mg/dm2/hr.while that of the control(lack of P in sand culture)is only 2.38 Co2mg/dm2/hr.similarly,rate of the trees under irrigation is 1.84 Co<sub>2mg/dm2/hr.with those of the control are 0.54 Co2mg/dm2/hr. Among the chestnut varieties cultivated in this intitute,differences in photosynthetic intensities are also discernible.