To provide reliable data on the indoor environment in livestock buildings, continuous measurements were conducted in two commercial naturallyventilated pig weaner barns in eastern China. The barn floors were partiallyslatted and pig manure was removed daily. Indoor temperature and relative humidity (T and RH), and concentrations of carbon dioxide (CO2), ammonia (NH3), hydrogen sulfide (H2S), and methane (CH4) were continuously measured with multipoints monitoring for one year. Hourly means of barn T and RH were ranged from 0.9℃ to 42.0℃ and 31.1% to 97.7%, respectively. Hourly mean CO2, NH3, H2S, and CH4 concentrations were ranged from 423mg/m3 to 3534mg/m3, 0.11mg/m3 to 49.7mg/m3, 0.9μg/m3 to 41.7μg/m3, and 0.1mg/m3 to 17.7mg/m3, respectively. The yearly average barn T and RH were (25.6±8.6)℃ (yearly mean ± standard deviation) and (71.4±11.7)%, respectively. The yearly average CO2, NH3, H2S, and CH4 concentrations were (1.982±744)mg/m3, (10.9±8.4)mg/m3, (8.2±5.2)μg/m3, and (2.9±1.9)mg/m3, respectively. Diurnal and seasonal variations of T, RH, and gas concentrations were clearly shown. The minimum and maximum hourly mean T and RH, and the maximum hourly mean CO2 and NH3 concentrations exceeded the relevant China National Standards for commercial pig weaner barns. However, the maximum H2S and CH4 concentrations were at safe levels for animal health and barn safety. The longterm highfrequency monitoring system has been approved as an appropriate technique for assessing air quality and environmental condition in animal building, the results also indicated that piggery housing system design and ventilation system optimizing still need further exploration in eastern China.