This study examined the effect of biochar addition on nitrous oxide (N2O) emission and nitrogen (N) transformation in co-composting of biochar and chicken manure. Compared with the control (no biochar), addition of 20% biochar resulted in a 59.8% decrease in the major peak of N2O emission. Ammonium (NH4+-N) and nitrate (NO3--N) contents in the final product with 20% biochar addition increased by 67.3% and 66.7%, respectively, compared to the control. Turning frequency (TF), the primary parameter of aeration and temperature control in the biochar-manure co-composting process, was also investigated. Results indicated that less frequent turning (e.g., turning every seven days) promoted NH4+-N and NO3-N retention but increased peak N2O emission by 58.1% compared with daily turning. Overall, biochar can be an ideal bulking agent for stabilizing N-rich materials to minimize N2O emission and, with proper aeration, can enhance nitrogen retention based on this laboratory study.