Discoloration mechanism of ABS molding containing silver as an antibacteria agent was investigated. FTIR and GC-MS spectra were mainly measured for discolored part, extracts from the discolored part with n-hexane and discolored components isolated from the extracts with TLC. In the present study (1-Naphthyl, 2 (-α-Methyl) acetracene ethyl silver cyanide) could be extracted from the discolored parts. Furthermore, amount of radicals formed in the molding was compared by ESR measurement of the uncolored and discolored parts. Based on the above examinations, discoloration mechanism was proposed in such manner where silver added to the molding as the agent easily reacts with fatty acids, such as cholesterol metabolized from a human body, to form a silver complex because of its high activity, resulting in discoloretion of the molding in purple.