A combination of ethylcellulose and pectin, when applied as a film coat, has a potential value as a colon-specific delivery system. Dispersions of pectin in ethylcellulose were used as the film former for coating of 5-aminosalicylic acid (5-ASA) pellet cores. Drug release behavior was assessed, in vitro, under simulating conditions in term of pH and time in vivo during transit to the colon. Negligible drug release occurred during first 5 h, when the coated pellets were in the simulated gastric and small intestinal conditions. After that, rat cecal contents were added into the pH 6.8 medium to simulate the in vivo condition where there is the digestion of bacteria in the colon. Drug release depended on the composition of the mixed film, as well as the ratio of ethylcellulose to pectin. Drug release profiles seemed to conform to the mechanism involving the osmotically driven release and formation of channels in the film caused by dissolution of pectin. Channel formation was, in most cases, activated by the presence of rat cecal contents, showing that the pectin in the mixed film was subjected to enzymic breakdown. In conclusion, pectin could be used as an additive in ethylcellulose films to control the release of colonic delivery system. In addition, the mechanism of the hydrophilic drug release from pellets coated with ethylcellulose aqueous dispersions containing an aqueous gel-forming polymer (pectin) is also discussed.