Organic wastes, such as activated sludge, obtained from solid waste purification plants of city municipalities are used for organic carbon and nutrient sources to the soil. Moreover, the origin, amount and nutrient contents of activated sludge are important for soil microorganisms. Activated sludge collected from domestic and industrial waste plants of Adana, Osmaniye and Gaziantep were added to peanut soil at three doses of sludge (2, 3 and 4 g/100 g oven dried soil) to compare carbon and nitrogen mineralization. Experiments were run at 28 degrees C over 45 days. Carbon (C) and nitrogen (N) mineralization was measured in vitro. The highest microbial activity and carbon mineralization ratio was observed in soil mixed with 4 g industrial activated sludge of Gaziantep. Increasing doses of industrial activated sludges of Osmaniye and Gaziantep decreased nitrogen mineralization. These results might be explained by the origin and composition of industrial activated sludge of especially Gaziantep city and organic carbon and nitrogen in it.