A system for the controlled release of one or more physiologically or pharmacologically active substances, comprising compositions in the form of micro particles or granules, particularly for use in the zootechnical and/or veterinary field. The micro particles include a core which contains one or more substances having a pharmacological action, food supplements or diagnostic media, said one or more substances being characterized by the presence, within their chemical structure, of a basic functional group, specifically including an amine functional group. The core comprises also one or more carboxylic acids and/or their salts and eventually one or more excipients. Said core is coated by an outer layer of fats or waxes, and preferably by a mixture of glyceride of fatty acids.