This research aims to investigate Park Kilyong’s architectural theory and critique of Gyeongseong (Seoul) buildings, expressed in his ‘Overview of Modern Buildings in Gyeongseong’ and ‘Critique of Gyeongseong Buildings’ (Samcheolli, Sept. and Oct. 1935); and ‘Architectural Form of the 100% Function’ and ‘The Modern and Architecture (1)-(4)’ (Dong-A Daily, 28 Jul. to 1 Aug. 1936). As a result, it is confirmed that Park had the functionalist theory of modern architecture, which suggests that Korean architects of the Japanese colonial period were accommodating the contemporary trend of world architecture. However, Park shows his fundamental limitations in the fact that the main content of his articles was a verbatim translation of two Japanese references (Kurata, 1927; Ishihara, 1929) without proper indications. Despite the limitations, his texts are still meaningful since he formed his own architectural theory on the basis of what he translated; and indeed his critique of Gyeongseong buildings, however simple, was based on the theory. This research makes a critical analysis of Park’s functionalist theory from both the 1930s’ and present points of view and compares his commentaries on Gyeongseong architecture with those by Ko Yu-seop (1932) and Hong Yunsick (1937), illustrating how Korea perceived architecture and modernism in 1930s.