The peculiarities of leaf carbon dioxide gas exchange in soybean genotypes grown in field over a largearea and contrasting in duration of vegetation, photosynthetie traits and productivity were studied.Varietal differences in the daily and ontogenetic changes in photosynthesis and photorespiration wereidentified. It was established that the period of the high activity of photosynthetic apparatus in highproductive soybean genotypes lasts for a longer time. The photosynthetie rate and the rate of CO, re-lease in light due to photorespiration are higher in high productive genotypes. The magnitude of plho-torespiration in contrast soybean genotypes constitutes about 28-35% of photosynthetic rate. The ratiobetween true photosynthesis and photorespiration in genotypes with different productivity is constantenough during ontogenesis, indicating a direct positive correlation between true photosynthesis andphotorespiration.