Abstract: The objective of this study is determining the optimum conditions of co- composting of dewatered sewage sludge and sawdust. To perform this study, the dewatered sewage sludge with humidity between 78-82% was mixed with sawdust. Turning over did once a week for aeration. Temperature was monitored at different depths daily. Other parameters such as N, C, organic matters, pH, heavy metals, total and fecal coliform and Salmonella were determined three times a week. The results of this study showed that after about 15th days, temperature of the mixture reached up to 55°C and was stabled for 15 days. Percent of dry solids increased from about 37.87 to 66.58%. At present study, a C:N ratio of 26.63:1 is considered and at the end of composting period reached about 20.52:1. Microbial parameters such as total and fecal Coliforms and Salmonella decreased significantly at the end of composting period so, the number of total and fecal Coliforms and also Salmonella decreased to A class standards of US EPA at the end of the operation. The computed correlation coefficients and the p values show a significant correlation between reduction of organic content and microbial parameters (R2 = 0.91, p<0.001). Also, organic matter and organic carbon of the mixture decreased during of the study, due to increasing the temperature. The result indicated that co-composting of sewage sludge with sawdust is a reliable and simple method to schedule, with high flexibility and low odor production. Organic compounds and pathogenic microorganisms reduced and EPA standards were met during this method.