In 1923, the Japanese colonial government replaced most civil and commercial laws in Taiwan with those of Imperial Japan, with the exception of legislations related to family and succession affairs, which still followed the norms in the prevailing Taiwanese Kazoku customs. Hence, the modernization or Japanization of laws for Taiwanese family and succession affairs were comparatively less apparent. As a result, controversy arose as to the extent of Japanization concerning Taiwanese Kazoku customs. This paper re-examines this issue through a critical review of primary data collected from related precedents of both Appellate Court and High Court of Taiwan. Analysis of the data revealed that Taiwanese Kazoku customs were indeed subjected to influence from Japan as well as the West. Starting from the 1910s, the Colonial Court introduced elements of Japanese family and succession laws indirectly through legislations related to household registration or through re-interpreting 'old' Taiwanese Kazoku customs. Such tendency became more intense and obvious in the 1930s and had much to do with the actual legal practice in local courts. In addition, the knowledge gained in the legal reform movement of the 1920s as well as the enactment of Taiwan Koseki Law and the Kominka movement in the 1930s all contributed to such tendency. With the defeat of Japan in 1945, the Japanization of Taiwanese Kazoku customs came to an abrupt end as an unrealized dream of inland extension.