This study applied the well-developed theory of planned behaviour (TPB) to investigate environmental activism behaviour concerning country park development in Hong Kong. A structural model was developed that incorporates the construct of human rights (HR) awareness into the basic model of the TPB. A questionnaire on HR awareness and TPB factors was developed, and data from 607 participants were collected through a telephone survey. Statistical analysis was carried out via structural equation modelling using AMOS 24.0. The results of the study showed a positive relationship between HR awareness and environmental activism behaviour. The proposed model with the construct of HR awareness showed improved explanatory power and model fitness compared to those of the basic model of the TPB, successfully confirming the predictive power of HR awareness on environmental activism behaviour and showing theoretical improvement in the TPB model. This study found that those who showed a stronger degree of HR awareness in terms of civil and political rights were more eager to support and engage in environmental activism. This result may be particularly insightful in light of the Hong Kong government’s perceived lack of transparency and accountability in environmental policy-making, which in recent years has put environmental conservationists and human rights supporters on the defensive front amid their heightened campaigns of environmental activism. Moving forward, future studies of HR awareness and environmental activism can be extended to include other types of rights, such as economic, social and cultural rights.