In this study, composting of olive pomace from three-phase oil production system, sewage sludge, dairy manure, and tomato stalks were carried out. The effects of carbon/nitrogen ratio on decomposition rate of composting were investigated with constant free air spaces of composting mixtures. Composting process was carried out in the aerobic reactors made of stainless steel which were monitored for 32 days. Temperature-controlled feedback system was operated based on the Rutgers strategy. Temperature, moisture, organic matter, pH, electrical conductivity total carbon, total nitrogen, ammonium nitrogen and nitrate nitrogen, total phosphorus as well as potassium were monitored during the composting process. In addition, mass and volume changes of the mixtures were determined. The highest degree of decomposition was determined for the mixture (carbon/nitrogen ratio of 20) based on the dry matter loss where the maximum amount of sewage sludge was used. On the other hand, maximum decomposition occurred at a carbon/nitrogen ratio of 23 for mixtures containing dairy manure. The increase in the use of olive pomace in mixtures had adverse effects on the decomposition process. The stabilization process in the mixture containing dairy manure lasted shorter than the mixtures containing sewage sludge.