The success of a new product development project generally means faster and more complete commercialization, market launch, and generation of financial returns. The process of achieving commercialization success involves many stages, and the level of cross-functional integration required at each stage differs. This study examines changes in the level of integration required at each stage, identifies variables that influence the required level of integration, and investigates the impact of the appropriateness of actually achieved integration on the technical and financial success of projects. The research subjects were new product development projects that received the Jang Yeong-sil Award from 1991 to 1998. The analysis results show that R&D-production integration is most required at the process development stage, while R&D-marketing integration is most required at the commercialization stage. The level of integration showed significant differences depending on the nature of the project's core technology, the type of development, the novelty of the new product market, the competitive conditions of the market, the speed of technology, and the difficulty of the technology. Regarding the impact of integration appropriateness on performance variables, the better the R&D-production integration, the shorter the stabilization period. The better the R&D-marketing integration, the higher the overall efficiency of the project duration. No statistically significant relationship was found between the appropriateness of cross-functional integration and financial performance. Since this study analyzed individual projects, it has the limitation of not fully elucidating the relationship between the appropriateness of each cross-functional integration and performance. Based on the results of this study, future research can expand and further develop cross-functional integration research by using the research laboratory as the unit of analysis to study integration across all functions throughout entire projects.