Flipped classroom focuses on the design of cooperative learning activities and allows them to be applied to a training. This study aims to develop a flipped classroom in diving environment training for rescuers and obtain results to assess their feasibility. The development steps taken refer to the multimedia web-based learning design combined with the PEDATI model at the design stage. The feasibility test is obtained based on the assessment of experts including material experts, learning design experts and media experts as well as suggestions and input from students after completing learning, as well as conduct pre-test and post-test to see the level of effectiveness through learning outcomes.The results showed that the design and development were in accordance with the steps and procedures that had been planned and the results obtained from the feasibility test that this learning was feasible to use and the effectiveness test with the criteria was effective enough to improve student learning
outcomes.Keywords: flipped classroom; online learning; diving environment; training.