Abstract: A colon selective pharmaceutical composition for oral delivery of one or more therapeutically active substances, comprises (i) a matrix core having the active substance or substances dispersed therein, and (ii) an outer cover layer without any active substance, said matrix core and cover layer being selectively degradable by enzymes normally occurring in the colon. A method of preparing such a colon selective pharmaceutical composition comprises the steps of mixing at least one therapeutically active substance with a matrix material to prepare a matrix core having the active substance or substances dispersed therein, and coating said matrix core with a material without any active substance therein to provide the matrix core with a drug-free protective cover layer, said matrix and cover layer materials being based upon at least one substance which is selectively degradable by enzymes in the colon.