A three-factor, three-level Box-Behnken design was used to study the rotary fluidized-bed aqueous coating process. 10% theophylline-containing granules were made, dried and subsequently coated in a rotary fluidized-bed. Based on the experimental design, the factor combinations resulted in different theophylline release rates and profiles. An optimization attempt was made to achieve a maximum amount of drug release after 11 h. The percent dissolution-time profiles were found to be significantly affected by the coating temperature and spray nozzle pressure. Theophylline release rates were found to be linearly affected by the polymer amount. Overall, the rotary fluidized-bed was found to be an efficient piece of equipment for granulating and coating processes.