An experimental study was carried out on an insulated MS reactor of total length 1650 mm and constant diameter 76 mm for updraft gasification of jute stick particles with air as the gasifying agent. The results and performances were evaluated for different sizes of jute stick particles at various superficial air inlet velocities ranging from 0.0337 to 0.1011 m s(-1) at STP. Accordingly, the superficial mass velocities of solid particles were changed from 0.0225 to 0.0950 kg/(m(2) s(1)). The calorific value of the producer gas was found to be in the range of 4306-4912 kJ Sm-3. An attempt was made to develop a predictive model of the gasification system. Gas diffusion through the solid pores was postulated to be controlling the rate processes in the developed non-equilibrium, mechanistic model. Approach to solve the governing equations was analytical and the total process was found to be controlled by a few dimensionless numbers containing the process variables. Comparison of experimental data and the model predictions indicated the validity of the model under the given circumstances.