A phenomenon efficiency dropping by many environmental factors, we call it weathering and it is evaluated by weathering test. It tests the effects of environmental factors to materials or structures as time goes by. Generally, we do outdoor weathering test and lab weathering test at the same time because lab weathering test cannot copy of all the factors at natural environment and outdoor weathering test has problems such as several of environmental factors, long test period, and reproducibility. We study about the correlation between outdoor weathering and Lab weathering test results on the exterior paint.