The properties of photopolymer printing plates subjected to artificial aging processes were investigated with differential scanning calorimetry and microscopic analysis. The results showed that exposure to extended ultraviolet radiation type C in the prepress process caused changes both in the thermal properties and in the structure of the outermost surface layer. Long exposure to ultraviolet radiation type A in a weathering tester led to structural changes at a deeper level and a simultaneous increase in the glass-transition temperatures of the polymeric material. Spectroscopic analysis showed that extensive oxidation occurred in the outermost surface layer. This study provides insight into important aging processes of the photopolymer printing plates. The knowledge can be used to predict the lifetime of printing plates and to understand the effects of their aging on print quality. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 1636-1646, 2009