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