ABSTRACTPreconception counseling can improve women’s health and pregnancy outcomes. Internal health locus of control and belief in the benefits of health-promoting behaviors improve people’s engagement in health-promoting behaviors. This study examined whether preconception counseling was related to stress and health locus of control. This randomized controlled trial was conducted from March to November 2016 on 152 healthy 18–35-year-old women intending to become pregnant within the next year in Iran. The intervention group received six sessions of group counseling, and the control group received only usual care. The Perceived Stress Scale, Multidimensional Health Locus of Control Scales and checklist for preconception control were completed before and after the intervention. Repeated measures ANOVA showed a significant post-intervention increase in the mean internal health locus of control (P < .001) and preconception control scores (P = .034) in the intervention group and the mean perceived stress score (P = .001), and chance health locus of control (P = .013) decreased significantly. Preconception counseling was associated with increased internal locus of control and reduced perceived stress. Preconception counselors should consider reinforcing women’s internal beliefs with an emphasis on the effect of the couple’s own behaviors and exposures on pregnancy and fetal outcomes.