Over the past decade, the ratio of annual official listing in Taiwan between used cars and brand-new cars is 2:1, to show that car users increase the acceptance for used cars, also show that the market of used car in Taiwan will be expect with car dealers. However, there exist an asymmetric information situation in used car market for a long time, and it also the primary concern with consumers. Recently year, local used car dealers provide the certified system with used cars, through over hundred standardized inspections to certify the used car. Used car dealers expect to decrease the purchase risk with the concept of service innovation, and enhance the confidence in the minds of consumers. In this research, service innovation will compare with perceived risk-six dimensions from Peter & Tarpey in 1975. The goals of this research are find the mediator effect within service innovation, perceived risk and purchase intention, and the relationships between service innovation and purchase intention in certified used car market. Samples of 158 collected through questionnaire survey, verified the hypotheses by description statistics and regression analysis. The results showed that have the significant relationship between service innovation, perceived risk and purchase intention in certified used car market, moreover, the three variables did have the partial mediator effect. Base on the results, the suggestion for certified used car dealers as followed: dealers should provide multiple innovative services with customers, to decrease the perceived risk and enhance the purchase intention in the future.