不同於其他民商事項在1923 年後改依日本民法，日治時期臺灣人家族事項始終「依用舊慣」或「依習慣」，因此有關臺灣人家族法的日本化問題，成為值得探討的問題。有學者認為日治後期有明顯日本化傾向，亦有學者認為日本當局並未致力於臺灣人家族習慣的日本化。 本文以總督府法院的覆審、高等法院判例集相關案例為主要資料，重新檢討此一問題。本文認為日治時期臺灣人家族法確實有日本化的傾向。總督府法院在1910 年代即透過戶口規則及舊慣立法草案精神，間接引進日本家族法元素；而在進入1930 年之後，日本家族法的影響更為顯著。此一日本化趨勢背後的原因，與總督府法院的實務考量有關。除此之外，包括總督府法院在1920 年代末期修法運動累積的知識基礎，以及1930 年代臺灣戶籍法制的實施及皇民化運動等大環境，也有助於此一趨勢的發展。但此一日本化的趨勢，最後因為日本的戰敗而變成未竟的內地延長。

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.