The chitosan microspheres were prepared by a membrane emulsification method with variations of the N-2 gas pressure and the chitosan concentration. The pressure of N-2 gas was varied within the range from 0.2x10(5) to 0.8x10(5) Pa at chitosan concentration 1.5 wt%. In addition, the concentration of chitosan was varied between 0.5-2.0 wt% at 0.4x10(5) Pa of N-2 gas pressure. Using this method, it is possible to prepare stable emulsions with a very narrow droplet size distribution in comparison with conventional methods. The average size of the microspheres was dependent on the N-2 gas pressure and the concentration, that is it was increased with the pressure and the concentration. The modelling of the size for the microspheres according to the concentration was carried out using Macleod's relation and Parkins & Brown equation. The former shows the relationship between density and surface tension and the latter demonstrates the correlation between the volume of the microspheres and the interfacial tension. The modelling results were in good agreement with the experimental data to predict the microspheres size with the variation of concentration.