New product development (NPD) is a complicated task which requires cooperation among multiple functional units, while the evolution of NPD systems is accompanied by an evolution in the integration domain. Mergers & Acquisitions (M&A) may alter positions between competitors and partners, as the resources and core competence that competitors own may be internalized through integration to become competitive advantages of the acquiring company. This study examines the benefits and effects of post-merger integration on NPD performance, and the analysis includes confirmatory factor analysis (CFA) and structural equation modeling (SEM). The analytical results indicate that there exists a positive correlation between external integration and internal integration. Although external integration is positively related to new product competitive advantage (NPCA), internal integration is not positively correlated with NPCA. Furthermore, shared product vision is positively correlated with NPCA and NPD performance, and NPCA is positively correlated with NPD performance. In addition, an examination of the mediation effect in terms of the Sobel t test indicates that NPCA significantly mediates the influence of integration on NPD performance. Furthermore, this study provides a framework for managing post-merger integration and concludes by discussing the theoretical and practical implications of the research findings.