The kinetics of hydrogenation of acetophenone was studied using a 10% Ni supported on zeolite Y catalyst in a temperature range 353-393 K, The effect of H-2 pressure, initial concentration of acetophenone and catalyst loading on the concentration-time profiles was studied. Water formed during the course of hydrogenation showed a strong inhibiting influence on the rate of reaction. A rate equation has been proposed based on GH type rate mechanism assuming that the reaction between the noncompetitively adsorbed hydrogen and the adsorbed organic substrate as rate Limiting step. A semi-batch reactor model was developed to predict the concentration-time, H-2 consumption-time profiles at different sets of initial conditions. The model predictions were found to agree with experimental data very well at all temperatures. This model incorporates the inhibition of hydrogenation rate due to water. The inhibiting effect of water is also explained based on quantum chemical calculations.