Several experiments were conducted for the purpose to know the role of the leaf photosynthetic rate playing on the dry matter production in corn plant. The leaf photosynthetic rates among 4 varieties of corn were measured changing radiation levels at 3 different growth stages. At the same time, dry matter production of each variety was measured under controled LAI by changing pot intervals. Results obtained were as follows. 1. The rate of leaf photosynthesis was different among varieties. Some varieties attained high capacity at intensive radiation level, while others saturated at relatively low light intensity. 2. Generally, the maximum rate of leaf photosynthesis decreased according with the advance of leaf age and piling of leaf layers. But varieties which adapted to low light intensity attained higher dry matter production. 3. Positive relationships were observed between NAR and rate of leaf photosynthesis at any growth stages. Especially, the photosynthetic rate of the newest fully expanded leaf at 60 Klux of radiation and NAR was closely correlated during early vegetative stage, while during active vegetative stage, between one at 10 Klux of radiation and NAR existed high correlation. These suggest that photosynthetic capacity at low light level plays rather important role for dry matter production especially under well grown canopy.