Abstract: Abstract: A dramatic increase in the amount of chicken manure is posing a great challenge on the social community, ecological environment, and human health, as the growing demand of chicken meat and eggs in China. Fortunately, composting process is an effective, sustainable, economic and natural way to recycle the decomposed organic materials, with an emphasis on the manure treatment prior to land application. Nevertheless, there are usually lots of odor emissions during the composting of nitrogen-rich chicken manure. The C/N ratio of raw materials markedly determines the compost maturity and the odor emissions during composting. At present, lots of previous studies focused on the effect of C/N ratio on the compost maturity and quality. However, only a few reports paid attention to the odor (NH3 or H2S) emissions during chicken manure composting. In this study, three C/N ratios, including 14, 18 and 22, were selected from the co-composted chicken manure and cornstalks as the bulking agent, to improve the compost quality, while decrease the odor emissions. An attempt was made to explore the comprehensive effect of C/N ratio on maturity and odor emissions (NH3 and H2S) during chicken manure composting. The aeration was in an intermittent mode (Sated 30 min, stopped 30 min), and the rate was 0.2 m3/h. The composting lasted 35 days, where the sampled on the day of 0, 3, 7, 14, 21, 28, 35, respectively. The basic physicochemical and maturity indexes were measured, including temperature (T), oxygen (O2), inorganic nitrogen content (NH4+-N, NO3--N), pH value (pH), Electrical Conductivity (EC), C/N ratio, Germination Index (GI), and the element content (C, N and S). Odor emissions (NH3 and H2S) were continuously monitored daily. A canonical correspondence analysis (CCA) was also used to analyze the microbial community composition, as well as their correlation with physicochemical indexes and odor emissions. The results showed that the final compost with the C/N ratio of 14 was not mature, while both the treatment with the C/N ratios of 18 and 22 reached the maturity standard. In terms of odor emissions, the C/N ratio of 18 treatment had the highest NH3 emission, because of the higher degradation of organic matter. When the C/N ratio ranged from 18 to 22, the NH3 emission and total nitrogen (TN) loss decreased with the C/N ratio increased. In addition, the cumulative H2S emission and the total sulfur (TS) loss were the highest in the C/N ratio of 14 treatment, while those in the C/N ratio of 18 and 22 treatments greatly decreased, indicating no significant difference. Moreover, the C/N ratio of 18 treatment had the highest microbial diversity, compared with other two treatments during the whole composting period. Furthermore, the microbial community compositions in the C/N ratios of 14 and 18 treatments (Firmicutes) were significantly different from those in the C/N ratio of 22 treatment (Actinobacteria and Firmicutes). More importantly, the CCA showed high temperature, high pH, and hypoxic environment can be beneficial to the proliferation of Firmicutes, and thereby to promote the emission of H2S and NH3. In an opposite case, high abundance of Actinobacteria can decrease the H2S and NH3 emission. As such, the recommended C/N ratio was 18~22 during co-composting of chicken manure and cornstalk. Specifically, the appropriate ratio can also be determined according to the number of cornstalks.