Background: Competency of nurses is a critical component that drives the quality of healthcare. Investigation of required competencies among nurses in particular context is essential to foster nursing services. Objectives: The aim of this article is to share the researcher’s experiences and give out explanations of the application of the Critical Social Theory through investigating nursing competency in context of Vietnam. Methods: An ethnography approach with data collection methods of participant-observations, in-depth interviews, and focus group discussions was conducted. Critical Social Theory was applied as theoretical foundation in order to gain deeply and fully understanding competencies of nurses. Results: It’s shown that using the Critical Social Theory as a theoretical foundation to investigate nursing competency in Vietnam context is applicable. This Theory is a school of thought whose primary goal is to improve the human condition. The theory focuses on general theoretical problems, as well as specific studies of concrete problems of contemporary social organization. The tactic focused on breaking with traditional hypothetical deductive methods, which are oriented towards the preservation and gradual reformation of the status quo. Its intention is to be a radically different approach which would consider the human construction of social forms of life and the possibility of their recreation. By applying the theory, it allows the researcher to explore and deeply understand what nurses think and act. Conclusion: To hear all nurses’ voices and smell the meaning of their behave in order to gain a rich and fully understanding of competencies of nurses, the Critical Social Theory is a suitable choice.