Composting is an effective waste management technology for converting animal wastes into valuable organic fertilizer. However, air emissions from composting, especially ammonia (NH3) emission, reduces the nitrogen fertilizer value of the compost and greatly impacts the environment. Ammonia emission from commercial composting facilities is not well understood and is limiting mitigation or recovery of NH3 emission from these facilities. The goal of this study was to determine the NH3 emission from a poultry manure compost facility and its temporal variations for development of mitigation strategies. A commercial composting facility was chosen for this study. Manure was supplied from four adjacent manure-belt layer barns. The composting building was tunnel ventilated by four 122-cm exhaust fans. Ammonia concentration at the building inlet and the fan exhausts was monitored quasi-continuously for one month in each of the four seasons using a MSA photoacoustic NH3 analyzer. Air temperature and humidity at the exhausts were monitored using a HOBO temperature and RH sensor and data logger. The exhaust fans were calibrated using FANS units to quantify the ventilation rate of the building. Ammonia emission rate was calculated according to the NH3 concentrations and building ventilation rate. The daily average NH3 concentrations at the exhaust of the compost house varied from 123 ppm in spring to 167 ppm in summer. The daily average NH3 emission rates of the compost facility varied from 231 kg/d in spring to 315 kg/d in summer. Strong diurnal variations exist in spring and summer seasons. Daytime NH3 emission is significantly higher than that of nighttime. The annual NH3 emission rate of the composting facility was estimated as 96,143 kg. The emission factors were calculated as 13±1.3 kg/ton · d and 0.32 ±0.14 g/d · hen. The results of this study will contribute to the development of NH3 emission mitigation technologies and management practices.