A field experiment was conducted during late rabi. 1995-96 to study the effect of moisture stress during post anthesis period in four rabi sorghum genotypes under three plant densities. With the increase in plant density there was a decrease in photosynthetic rate (from 10.77 to 8.8C µmole co^-2ms^-1) and transpiration rate (from 1.91 to 1.54 µ mole H₂Om^-2s^-1) per plant while the diffusive resistance was increased (from 16.25 to 20.23 sec cm^-1). Among the genotypes, voth 9-13 and M-35-1 showed, highest photosynthetic rate (9 98 and 11.07 µ mole CO₂ m^-2s^-1 respectively) and least transpiration rate (1.44µmole H₂ Om^-2s^-1) and diffusive resistance (18.00 and 16.98 sec cm-1. respectively). However, only transpiration rate decreased significantly in all the genotypes with increase in plant densities, while all density levels showed significant decrease in transpiration rate during post anthesis period as the crop approached maturity stage.