This study investigated the optimum mixture ratio of greenhouse tomato plant residues, wheat straw, and separated dairy manures for composting. Five 127-L laboratory-scale bioreactors were used to investigate the effect of separated dairy manure addition on the composting process of a tomato plant residues-wheat straw mixture. The wastes were mixed at 5 different ratios during the trials and were then placed in the reactor. Whereas the C/N ratios of the material mixtures placed in the reactors were fixed at a level of about 31, the FAS values ranged between 24.56% and 32.64%. Temperature and CO2 measurements were made from the reactors during the trials along with organic matter and moisture content analyses.