Drowning is the third leading cause of death for children aged 0–4 years in many Asian countries, and is a serious but neglected health problem in low and middle-income countries (LMICs) like Bangladesh. In Bangladesh, drowning rates are 10 to 20 times more than those in other developed countries. The aim of the effectiveness of a mobile SMS intervention to improve the environmental knowledge of parents of children aged under five concerning the prevention of drowning. A cluster randomized community trial with 788 parents of children aged under five in a rural community of Bangladesh. Mobile SMS intervention for parents of children under five years concerning the prevention of drowning. Association in environmental knowledge of parents concerning the prevention of drowning between the baseline and immediate follow-up after the intervention, and after three months. There was a significant improvement in environmental knowledge in the intervention group compared to the control group at different at baseline, immediately after intervention and 3-months after intervention. The associated factors for drowning included the time (11:00am-2:00pm), lack of swimming ability, parents who were not aware about childhood drowning, unwanted ditches that were not filled in, lack of medical facilities, and lack of information through mass media for the prevention of childhood drowning. Special programmes and training could be increase knowledge about childhood drowning prevention in Bangladesh and should be broadcast on the radio and television networks.