Dairy freestall housing systems are becoming more and more popular in the United States and Europe. In order to investigate the correlations between the thermal environments and gas emission in this type of buildings, seven typical freestall dairy farms in Denmark were surveyed for temperature, moisture and contaminant gas, in addition to the aerial conditions of the buildings. The results indicated that the temperature and humidity in the naturally ventilated dairy cow buildings were affected by the outside thermal conditions and the livestock in the buildings. When the outside temperature is between 0～25℃, the inside temperature is usually 1～3℃ higher than outside temperature. The inside temperature and moisture content were found to increase approximately 0.8℃ and 1000 mg/m³, respectively for every 1℃ increase in outside temperature. The NH₃, CO₂, and CH₄ concentrations were affected by temperature and moisture content. During the day hours, the concentrations of NH₃, CO₂, and CH₄ were about 20% lower because of greater natural ventilation. There was no correlation found between N₂O and indoor thermal condition during the measurements.