Abstract: By using compost bioreactors, we studied nitrogen conservation in compost treated with urease inhibitor NBPT over a 25 day composting process of chicken manure and mushroom residue feed-stocks under controlled aerobic conditions. In this experiment, NBPT was added at the rates of 0.00 mL·kg-1 (non-NBPT, CK), 0.04 mL·kg^-1 (T1), 0.08 mL·kg^-1 (T2) and 0.16 mL·kg^-1 (T3). Results show that adding NBPT does not result in a substantive variation in temperature over 25-day composting. It also maintains a relatively stable pH during the thermophillic period (high temperatures greater than 50 ℃) of composting. Compared with CK, adding NBPT decreases urease activity during the 0~10-day initial composting, but significantly increases total nitrogen content in the late 10~25-day composting. After 25 days of composting, adding NBPT decreases nitrogen loss by 6.61%, 4.89% and 13.51% respectively in treatments T1, T2 and T3. NH₄-N content shows two peaks with alternating low-high trend in the duration of the experiment. For most of the time, NH₄-N content in NBPT treatments is lower than that of CK. During two increasing periods, CK exhibits higher velocity than the NBPT treatments. NO₃-N content is unstable during the increasing temperature and thermophillic periods. It is, however, obviously higher under NBPT treatments than under CK at the end of the experiment. This result indicates that adding NBPT could retard N conversion from urea-N (contained in chicken manure) to the NH₄-N, increasing NO₃-N content in finished compost products. NBPT plays a role in minimizing N loss via gaseous ammonia (NH₃) by potentially conserving N during composting.