BACKGROUND Mental Health problems are one of the leading disabilities worldwide. Individuals seeking help for their mental illness expect nurses to be cognisant of their needs without prejudice and discrimination. Existing evidences suggest a growing number of patient referral from primary healthcare to psychiatric consultations. This study aimed to explore primary healthcare nurses' knowledge and attitude towards mental illness and people with mentally illness. METHODS A cross-sectional study using the Mental Health Problem Perception and the Community Attitudes to Mental Illness questionnaires. Descriptive and multivariate regression using maximum likelihood procedures were applied. RESULTS Regression analysis showed significantly high correlation between knowledge and authotarianism (β = 0.775, p = 0.007) and moderate inverse correlation with social restrictiveness (β = -0.517, p < 0.001). However, no significant correlation with benevolence (β = -0.057, p = 0.181) was detected. Nurses with higher educational level were significantly associated with authotarianism attitude. CONCLUSIONS This is the first study examining knowledge and attitude of primary healthcare nurses in Brunei. The relationship between the study variables as well as demographic factors, in comparison to other countries, were discussed. Overall, negative attitude among nurses is still a challenging issue; therefore, developing re-education initiatives and increase contact time, especially for healthcare front liners with negative attitudes regardless of education level, to favour change of attitude, is important to foster holistic care to people with mental illness and promote mental health in the population.