Abstract: Pot experiment was conducted to asses the temporal effects on gas exchange characteristics of blackgram at different growth stages. Two blackgram varieties namely BARImash 3 and BINAmash 1 were sown at 10 days interval on August 26, September 6, September 16 and September 26 of 1999. At each sowing time, photosynthetic gas exchange characteristics were measured at vegetative, flowering, pod filling, early maturity, mid maturity and late maturity stages of blackgram. Varietal difference was minimal but sowing time had profound effects on gas exchange characteristics of blackgram. Photosynthetic rate was higher in blackgram leaf sown on August 26 with its higher stomatal conductance, lower intercellular CO2 concentration and higher mesophyll conductance. The highest respiration rate was recorded at pod filling stage and fluctuated widely over the sowing times. Photosynthetic rate of blackgram decreased with delay in sowing times and the lowest rate was observed on September 26 sowing. Gas exchange characteristics were the highest at flowering stage of blackgram and declined gradually with the advent of plant age.