The light and CO₂responses of photorespiration rate (R_p) of soybean (Glycine max) leaves were studied under 2% and 21% O₂. The results showed that R_p of soybean leaves increased almost linearly with increasing photosynthetically active radiation (PAR) when PAR was less than 600 μmol·m^-2·s^-1; R_p reached the maximum value of 12.69 μmol CO₂·m^-2·s^-1 when PAR was about 1200 μmol·m^-2·s^-1, and then R_p decreased with increasing PAR. The function relationship between R_p and PAR was constructed. The fitted result showed that the maximum value of R_p (P_pmax) was 13.42 μmol CO₂·m^-2·s^-1, and the light intensity corresponding to P_pmax was 1207.74 μmol·m^-2·s^-1. The fitted values were extremely in agreement with the measured values (P<0.05). As air CO₂ concentration (C_a) (0-1200 μmol·mol^-1) increased, R_p of soybean leaves increased firstly and then decreased. It reached a maximum value of 9.97 μmol CO₂·m^-2·s^-1 when C_a was about 600 μmol·mol^-1. The function relationship between R_p and C_a was also constructed. The fitted result showed that the P_pmax was 10.21 SymbolmA@mol CO₂·m^-2·s^-1, and the C_a corresponding to the P_pmax was 625.74 μmol·mol^-1. The fitted values also accorded with the measured values (P<0.05). Thus, it can be concluded that the constructed function relationships between R_p and PAR and between R_p and C_a would provide a powerful means for the quantitative study of photorespiration of plant leaves.