Relationship-specific investments (RSIs) are an important issue for Taiwanese OEM/ODM suppliers. Prior researches on this issue have primarily focused on economic rationality and overlooked sociological approaches. This study uses mimetic isomorphism perspectives and argues that frequency-based, trait-based and outcome-based mimetic factors each have important influences on the RSIs decision. Further, when firms face with greater performance aspiration gap, in order to reduce the uncertainty and enhance the legitimacy of decision-making processes, firms may enhance their mimetic isomorphism behavior. Using a sample of 161 Taiwanese OEM/ODM suppliers, we find empirical support for our developed theory.