This paper aims at identifying the compulsory criteria to select potential candidates for library successors in Vietnam. The research was underpinned by transformational leadership theory. Data was mainly from the twenty-three in-depth interviews which was informed by the emerging themes from the online survey in thirteen public and four academic libraries in the Mekong Delta, Vietnam. In the context of a country with only one leading Party such as Vietnam, four compulsory criteria include professional knowledge, leadership skills, moral practice and political ideology. Other required criteria are enthusiasm, years of experience, work commitment, age, and external relationships. Political ideology and moral practices were found to be the most important finding and contribute to an understanding of factors in succession planning which has not been discussed in the literature so far. This research provides potential successors with an awareness of desirable professional criteria to be the library leaders. This study also specifies evidence that candidates cannot automatically proceed to managerial positions without continuing efforts and self-improvement. Furthermore, the finding of the research contributes an assistance for library leaders in selecting qualified staff for future managerial positions. These criteria can be used as a reference point for other similar contexts like Vietnam.