The purpose of the present invention is to newly provide a method with which it is possible to appropriately evaluate the protective effect of an external preparation for skin such as a sunscreen cosmetic, particularly to evaluate how a UV-ray protective effect is affected by heat. This evaluation method is characterized by including (1) a step for forming a coating film of an external preparation for skin on a substrate, (2) a step for heat-treating the coating film of the external preparation for skin, and (3) a step for measuring the UV-ray protective effect of the heat-treated coating film of the external preparation for skin. The heat treatment is preferably carried out for at least one minute at a temperature of 30-70° C. The step for measuring the UV-ray protective effect preferably includes at least one selected from testing methods that involve comparing some kind of UV-ray protective effect with SPF measurement, UVAPF or PFA measurement, critical wavelength measurement, absorbance measurement, and transmittance measurement. This evaluation method can also be performed in vivo or in vitro.