INTRODUCTION A literature review has revealed an absence of studies investigating the knowledge and behaviour of teachers towards secondhand smoke (SHS). This study was thus designed with the following objectives: 1) Assess the knowledge of SHS among primary school teachers, 2) Determine their behaviour towards SHS, and 3) Identify any relationship between knowledge and behaviour of participants. METHODS A national cross-sectional study was conducted among a representative sample from 28 primary schools in all four educational zones of Mauritius in 2017. A self-administered questionnaire was used to collect data from primary school teachers. Data analysis was performed on 389 questionnaires. RESULTS The mean knowledge score was found to be 28.9 (SD=4.8), which is just above the threshold score (>27) for good knowledge. Less than two-thirds of the participants (63.2%) were in the 'good knowledge' category. The mean behaviour score was found to be 26.6 (SD=6.8), which is situated in the range for 'satisfactory behaviour' in terms of avoiding SHS. Pearson correlation testing revealed a significant association between knowledge of SHS and behaviour towards exposure to SHS. CONCLUSIONS This study showed that nearly two-thirds of teachers had good knowledge of the health dangers of SHS and applied this knowledge in their behaviour by keeping away from cigarette smoke.