In this paper, we discuss the “Galapagos syndrome” in the Japanese mobile phone industry from the perspective of organizational institutionalism. In general, the Galapagos syndrome emerged because the Japanese companies ignored the international standards and focused on domestic markets for product development. Organizational institutionalism explains the diffusions of technology-related international standards to achieve social legitimacy, rather than the mere compliance with technical requirements. However, Japanese firms were active in obtaining international standards. To explain this situation, we reviewed the studies on diffusion in organizational institutionalism. During the review process, there was confusion with the idea of isomorphism and this led to two ways of understanding it: isomorphism as homogeneity and as the origin of competition. By revisiting the pioneering theory of organizational institutionalism by Weber, we can explain the Galapagos syndrome on the basis of the latter understanding of isomorphism; that is, the incorporation of international standards creates competitive relationships between the Japanese firms. By rearranging the logical implications to explain isomorphism and standards, we can conclude that the Galapagos syndrome results from differentiated practices related to the incorporation of international standards.