Abstract: A comparative investigation was conducted on degradation behaviors of a spray-free polypropylene material between outdoor exposure at four national standard natural exposure places and indoor accelerated weathering under three typical artificial conditions. The correlation between the above two weathering behaviors was studied and the weathering factors were analyzed. The results indicated that there was no correlation observed in the color difference between the 12 month natural exposure at four testing places and the artificial accelerated weathering. However, a change in gloss for the tested specimens obtained from Qionghai and Lhasa indicated a good correlation with artificial accelerated weathering under the condition 1, and furthermore, the result from the natural exposure at Qionghai presented a much better correlation. The acceleration rate of laboratory weathering under the condition 1 was double in comparison with that from the outdoor exposure at Qionghai. UV irradiation and water were found to play critical roles in the weathering of spray-free polypropylene materials.