Exposure to environmental tobacco smoke (ETS) is widespread among women in Iran. This study aimed to explore the impact of education on health belief and environmental tobacco smoke exposure in pregnant women. This randomized trial was administrated to 130 pregnant women exposed to ETS. The face-to-face education was provided for the intervention group after completing the questionnaire compiled on the constructs of the health belief model and self-reports of weekly ETS exposure. The theoretical constructs and weekly ETS exposure were compared in the study groups at the intake, third, fourth and fifth sections. In intervention group, perceived susceptibility/severity and perceived benefits increased and the weekly ETS exposure decreased on the third as opposed to the first section (P < 0.05). Perceived susceptibility/severity and benefits significantly correlated with weekly ETS exposure in the intervention group (P < 0.05). The findings of this study point to the fact that education about the impacts of ETS exposure of pregnant women is an effective way to increase the theoretical constructs according to the health belief model and is associated with a reduction of ETS exposure. But this is not sufficient for making smoke-free homes.