Sustained release cellulose acetate butyrate (CAB)-polystyrene (PS) microcapsules containing ketoprofen (a non-steroidal anti-inflammatory drug) were prepared adopting the modified W/O/W complex emulsion technique. The effect of polystyrene concentration and core/coat ratio on the yield, geometric mean particle diameter, dg, size distribution, drug loading as well as release and surface characteristics of the microcapsules was investigated. The results obtained revealed that polystyrene utilization as a wall material plays a dominant role in the manufacturing process. A particular composition of 92.5:7.5 (%) of CAB to PS was found to improve greatly the microcapsule yield and maximize the drug loading. In most cases, the encapsulation efficiencies increased with increasing microcapsule size and theoretical drug loading. Kinetic analysis of the data shows that the drug release process from CAB microcapsules followed Higuchi model (a diffusion-controlled model for a planar matrix), whereas the release behaviour conforms with Baker and Lonsdale model (a diffusion-controlled model for a spherical matrix) for CAB-PS microcapsules. The preparation of free films of CAB and CAB-PS was described for comparison. The effect of processing parameters (polystyrene concentration, total polymers concentration and permeant concentration) on the permeation of ketoprofen through the polymeric films was discussed. The results demonstrated that ketoprofen permeation through the films and microcapsules could be controlled by modifying the CAB-PS ratio in the polymer matrices. The permeability constants lowered with increasing total polymers concentration up to 5% and were proportional to permeant concentration. To compare the kinetics of drug release from polymeric films with those of microcapsules, ketoprofen was incorporated at different concentrations within CAB-PS cast films. These films exhibited sustained release of the drug (t(0.5); 58-146 h). Release rates were found to agree with the Baker and Lonsdale model, previously suggested for ketoprofen release from CAB-PS microcapsules.