Abstract:The stoma freguency and distribution on both epidermis of leaves of 65 species of C3 plants, 49 species of C4 plants and 16 species of CAM plants were studied by impres- sion method with colorless nail oil. The results indicated that distribution of stoma on both epidermis of leaves was in relation to the photosynthetic pathway and living type. The stoma ratio of upper/lower of C3 plants was 0.45 (sun herb) and 0.07 (shade herb), no stoma was found on upper epidermis of leaves of ferns, shrubs and trees. Plants with C4 photosynthetic pathway, except a few species, showed a higher stoma ratio of upper/lower 0.64 (Cyperaceae), 0.82 (dicot) and 0.94 (Oramineae). Much less stoma frequency was found in CAM plants than in C3 and C4 plant, but the stoma ratio of upper/lower was equal. In C3 crop plants, the species with shorter growth period and higher yield, such as sunflower, peanut and some leafy vegetables had higher stoma ratio of upper/lower. It is supposed that the stoma ratio of upper/lower might be used as an helpful index for identifing the C4 plants in monocot grass. It was also considered that the photosynthetic rate of amphistomatous leaves of C3 plants with same living type was related to the stoma ratio of upper/lower.