The study is concerned with the development of cellulose acetate microspheres by the o/w emulsification and solvent evaporation method in the presence of polyvinyl alcohol as an emulsifying agent. The influence of process parameters such as solvent mixture (acetone + dichloromethane) composition, concentration of the emulsifying agent and speed of stirring has been examined. The microspheres have been analysed for their size, drug loading capacity and release kinetics. Spherical and smooth surfaced microspheres with encapsulation efficiencies ranging between 73-98% were obtained. Use of acetone in the oil phase drastically reduced the particle size. Slow drug release from microspheres occurred up to similar to 8 h and the release was found to be non-Fickian. An optimization procedure was employed to investigate and identify the key parameters affecting the properties of the microspheres. A 3(3) randomized full factorial design was used in the analyses of the data. A linear model with interactive terms was generated using a multiple linear regression approach. The statistical analysis confirms the significant effect of solvent composition and concentration of emulsifying agent on the drug release characteristics.