There exist several issues in composting of chicken manure, tobacco wastes, and spent mushroom substrate, including slow temperature increase, low moisture reduction, gaseous emission, and long maturation period. Thus, this study aimed to address gaseous emission(e.g. ammonia(NH3) and nitrous oxide(N2O)) and increase product maturity in the composting of chicken manure and tobacco wastes with spent mushroom substrate as the bulking agent by adding nitrogen-conservation materials, which were 5% superphosphate and 10% biochar(based on wet mass of raw composting feedstocks). Results show that the temperature of all treatments could be maintained at 55 ℃ for more than 8 days to conform non-hazardous and sanitation standards. Compared with the control treatment, adding superphosphate and biochar could improve the compost maturity, while superphosphate increased the product salinity. Total nitrogen(TN) loss in the form of NH3 and N2O was reduced by 32.13% and 12.20%, respectively when 5% superphosphate was added. By contrast, such reduction was 28.83% and 34.15% with the addition of 10% biochar. Compared with biochar, superphosphate could be more effective to reduce nitrogenous gas emission and improve compost maturity during the composting of chicken manure, tobacco wastes, and spent mushroom substrate.