Introduction: Basic Life Support (BLS) has recently received special attention because the majority of cardiac arrests occur outside of the hospital, The advancement of technology with medical research contributes to evidence-based care for critically ill patients. This study aimed to evaluate the effectiveness of Basic Life Support (BLS) on knowledge, attitude, and practice among high school teachers. Materials and Method: This cross-sectional study was conducted among school teachers. A total of 112 participants were selected using a non-probability purposive sampling technique to evaluate the effectiveness of Basic Life Support (BLS) in terms of knowledge, attitude, and practice. A pre-test was conducted before the intervention and apost-test assessment was done at the end of the 5th day. Result: On the assessment of demographic variables, the majority of participants were found to be male (86, 76.8%), aged between 20 and 30 years (54, 40.2%), and postgraduate (87, 77.7%). The pre and post-test mean, SD, mean difference, standard error, and paired test were employed. On assessing the knowledge of school teachers, the mean difference between pre and post-test was found to be 1.82, standard error was 0.03, and paired t-test value was 50.1. Similarly, in attitude, the mean difference between pre and post-test was 1.92 and paired t-test value was 1.43. Analysis of practice skills showed that the mean difference between pre and post-test was 2.00, standard error was 0.00, and paired t-test value was 0.00. Conclusion: Basic Life Support (BLS) is a highly effective intervention for school teachers. Most of the school teachers improved their knowledge, attitude and practice after the intervention.