With an EARS--Plant photosynthesis meter we determined gross photosynthesis (P) of leaves of 'Cat Hoa Loc' mango on 4 years old trees planted in the Fruit Tree Experiment and Production Station, Campus 2, Department of Crop Science, College of Agriculture, Can Tho University in the rainy season of the year 2000. The same experiment was conducted on 'Nam Roi' pummelo on a farm located in the Binh Minh district, Vinh Long province. In the rainy season the calculated gross photosynthesis of 'Cat Hoa Loc' mango leaves at flowering stage was higher than that at the vegetative stage. However, the photosynthetically active radiation and quantum yield of 'Cat Hoa Loc' mango leaves in both stages did not reach the light saturation point when compared with values from estimated equation of photosynthetic light curve. The same holds true for 'Nam Roi' pummelo in the vegetative stage.