China is the largest swine production country in the world. The fast development has consequently brought various environmental issues which have already seriously threatened the environmental quality. This study is aimed to measure the concentrations of NH3 in the pig houses in the selected pig farm, try to conclude characteristics on the concentration change and the correlation between the concentrations and the environmental factors. The NH3 concentration was monitored in two fattening pig houses. The concentrations fluctuated between 11.0 and 26.9 ppm, 11.0 and 28.5 ppm respectively during the measurement periods, peaking at the early morning and in the afternoon before cleaning. The concentrations of NH3 correlated to the indoor temperature in winter, whereas, there was no correlation between relative humidity and NH3 concentrations.