Abstract: By utilizing compost bioreactors with dairy manure and mushroom residues as feedstocks under controlled aerobic conditions, nitrogen and sulfur transformation, compost temperature and nitrogen conservation were studied over a 21 day composting process by adding sulfur. In this experiment, sulfur was added at rates of: 0 (non-amended control, CK), 0.5% (T1, on weight basis), 1.0% (T2) with three replicates. Compared to the CK, the addition of sulfur at a rate of 0.5% (T1) has no significant effects on compost temperature, and the thermophilic period (temperatures greater than 50℃) is about 5.5 days, while, compost temperature is increased under the addition of sulfur at a rate of 1.0%, and thermophilic period is about 4.6 days. pH of compost is significantly decreased under the additions of sulfur, while ammonium nitrogen (NH+4-N) content is significant increased. For example, at the end of this experiment, NH+4-N contents of T1 and T2 are 15 and 24 times more than that of the CK, respectively. The extractable sulfur content is also significantly increased, and at the end of the experiment, extractable sulfur contents of T1 and T2 are increased by 35.7% and 77.1% compared to their initial values at the beginning of the composting. Slowly increased trend in total nitrogen content is observed during this comcomposting process. The total nitrogen contents are16.5 g/kg for T1, 16.9 g/kg for T2 and 15.8 g/kg for CK, with increases by 4.4% for T1 and 7.0% for T2. These results suggest that the additions of sulfur (0.5% or 1%) to the compost can significantly increase NH+4-N and extractable sulfur contents, and enhance nitrogen conservation, thus improving the quality of compost. Compare with the addition of sulfur (0.5%), effect of the addition (1%) is better, however, the thermophilic period is shorter and germination index is reduced, which are disadvantages for the harmless process of composting.