This paper examines the adoption process of Chinese legal codes from the Koryŏ to the Chosŏn periods and the subsequent changes of Korea’s legal system. Although Koryŏ organized its legal system based on the Tang code 唐律, it also adopted various other Chinese laws as needed. The Yuan 元 (1271-1368) demanded legal reforms from Koryŏ, but Koryŏ opposed, citing differences in social foundation. Eventually, the Yuan succeeded in prohibiting consanguineous marriage but failed in reforming the slave system. As a kingdom ruled by royal law, Koryŏ had weak legal stability, and so its society was in disorder. At the end of the 14th century, Koryŏ adopted the Great Ming Code 大明律to revise the legal disorder, and the legal code was carried over to the Chosŏn dynasty. The sixfold division of the Rites of Zhou 周禮 became the foundation of the Koryŏ government organization, and during the Chosŏn period, it became not only the basis for government organization but also a model for compiling legal codes. In the late 14th century, the adoption of Neo-Confucianism and Zhu Xi’s 朱熹 (1130-1120) Family Rituals transformed the gender-equal family structure into a patriarchal one. This transformation began with a shift from uxorilocal marriage to virilocal marriage and proceeded toward excluding women from ancestral rites and strengthening the inheritance rights of men and eldest sons. By the late 19th century, patriarchy was de facto established and was further reinforced during the colonial period. Furthermore, as time passed, many unique Chosŏn provisions that differed from the Great Ming Code emerged in criminal law, leading to its Chosŏn localization. However, Chosŏn emphasized ethical norms such as social status relationships more than China. The characteristic of adopting Chinese law in the traditional period was the proactive and autonomous adoption of those that fitted our needs. This approach remains meaningful even in the 21st century, when the world continues to integrate.