During the period 1955-1963, the government of the Republic of Vietnam selectively organized, institutionalized, and reinterpreted a number of traditional festivals - such as the Lunar New Year (Tết Nguyên Đán), the commemoration of the Trưng Sisters, the Qingming Festival (Thanh Minh), the Hung Kings’ Commemoration Day, and the Mid-Autumn Festival - within the framework of its cultural policy. Drawing on archival materials, contemporary press sources, speeches, and administrative documents, this study employs a historical methodology combined with discourse analysis and source criticism to examine how the state intervened in ritual organization, shaped symbolic meanings, and embedded political objectives within traditional cultural practices. The findings indicate that the utilization of traditional festivals under the Ngô Đình Diệm regime served not only the political competition with North Vietnam, but was also closely associated with efforts to construct legitimacy, mobilize social consensus, and project a national image in South Vietnam. Accordingly, the study contributes to a deeper understanding of the relationship between culture and power in modern Vietnamese history, while also clarifying the extent, modalities, and limitations of the politicization of traditional festivals under the Republic of Vietnam.