Abstract: CO2 emissions from liquid pig manure stored in under-floor pits were investigated using an empty full-scale pig house in Denmark in winter time. The experiment designs were of three manure depths of 0.15, 0.40 and 0.65m, three ventilation rates of 211, 650 and 1852 m3/h, and with or without pit curtains. The three parameters that explained most of the variability of the CO2 emissions were ventilation rate, manure temperature, and pit curtain. CO2 emission rate increased as room ventilation rate increased with diffuse ceiling inlet. There were significant differences in CO2 emission rates among three ventilation rates. CO2 emission rate and air exchage rate could be reduced significantly by using manure pit curtains. No significant differences in CO2 emission rates were found among three manure depths. The emission rates were more sensitive to manure temperature than to ventilation rate due to higher sensitivity percentages. At the lower ventilation rate ranges, the emission rates were more sensitive to ventilation rate change compared to the higher ones. However, the contrary sensitivity responses for different manure temperature ranges were obtained. Increasing ventilation rate could reduce the temperature of room and pit air as well as manure temperature, therefore, the effects of ventilation rate and temperature on gas emissions should be considered comprehensively.