A new test method for weatherability prediction of coatings using remote plasma reactor has been studied. We studied the degradation of coatings by radicals because we paid attention to the fact that exposure to radicals strongly influences the durability of coatings. As a means of direct radical irradiation on the coatings, we used a down-flow type remote plasma reactor, and investigated changes of not only color and gloss but also surface morphology through the weatherability of enamel type coatings. This remote plasma method showed extremely good acceleration in the degradation of the coatings and good correlation with outdoor exposure test performed in Okinawa. Conventional acceleration methods, especially the Super UV weather-test machine, resulted in changes opposite to outdoor exposures with the amount of titanium oxide pigment used. However, the use of remote plasma reactor enabled us to get the good correlation similar to the outdoor exposure.