My paper highlights the ways a population of Vietnamese people expresses strong dissent and takes action against decisions by policy makers to protect the environment. Recently, online environmental activism in Vietnam has been translated into street protests despite suppressive responses by the government at times. Moving from the background to the forefront of political scene, the environmental movement has become one of the most vocal forms of Vietnam’s civil society. By investigating environmental activism as an arena of contestation, and the involvement of concerned citizens, the paper seeks to contribute to a more comprehensive definition of civil society in contemporary Vietnam. In environmental aspect, Vietnam’s civil society has both formal and informal elements, which together trigger a new form of nationalism – a concerted display of concern and action for the environment. Accordingly, I argue that environmental activism in Vietnam, whether it carries political/oppositional or nonpolitical implications, challenges the legitimacy of the government, opens up a new era for people’s participation in the decision-making process and creates more space for participatory citizenship. As identified in this research, the hindrances to people’s practice of their environmentalism are the delayed law on ‘the practice of demonstration’, the state’s strict ways to police them, and a number of ‘civil society actors’ who tend to resort to violent action, rendering non-violent activism problematic. Ultimately, this research contributes to the understanding of social conflicts and tensions in Vietnam’s state-society relations, through the lenses of political ecology and environmental anthropology of people’s environmental activism.