Gasification of high-ash Indian coals having different proximate and ultimate contents is presented in this paper. Mathematical simulations of the gasification process in an updraft moving bed gasification system are reported. A steady one-dimensional mathematical model, which takes into account of drying, devolatilization, combustion and gasification processes, is used to solve the mass and energy balances in the gasification system. The results from the model have been validated against the experimental data for Indian coals available in literature. The predicted dry gas flow rate and its higher heating value are in agreement with experimental results. The validated model is used to study the effect of coal properties on gasification output. Air flow rate of 0.3 times the stoichiometric and steam to coal ratio of 0.4 are used in all simulations. Result reveals that carbon and ash content in coal pays an important role in gasification process. Increase in carbon content in coal increases the calorific value of gas, while increase in ash content reduces the calorific value. The model is useful for predicting the performance of high-ash Indian coals of different compositions in a moving bed gasification system.