Background and objectives <p>This study compares the impact of breastfeeding counselling based on the Information-Motivation-Behavior model (IMB) with routine counselling at the breastfeeding counselling center on certain health indices of mothers and their infants.</p> Methods <p>The present study is a clinical trial using a convenient sampling method conducted randomly on the referred mothers and their infants. Participants were allocated into two groups “routine counseling at the breastfeeding counseling center” and “breastfeeding counseling based on the Information-Motivation-Behavior Model” (59 mothers and their infants in each group). Demographic information, WHO breastfeeding observation form, latch assessment form, infant weight, maternal body mass index (BMI), blood pressure, and postpartum depression questionnaire were filled. Outcomes were reassessed at 2, 4, and 6 months of children’s age for both groups. The infant behaviour questionnaire was completed only at 6 months.</p> Results <p>The two groups were similar in terms of demographic variables and obstetric history, such as maternal education (<i>p</i> = 0.589), spouse’s occupation (<i>p</i> = 0.457), wanted/unwanted pregnancy (<i>p</i> = 0.154), and delivery type (<i>p</i> = 0.349). In the intervention group, significant differences were found compared to the routine counseling group in postpartum depression scores (<i>p</i>-value = 0.030), body mass index (<i>p</i>-value &lt; 0.001), latch assessment scores (<i>p</i>-value &lt; 0.001), and total WHO breastfeeding observation form scores (<i>p</i>-value &lt; 0.001). In this study, the results were in favor of the intervention group. These differences became observable from the second month, leading to the continuation of exclusive breastfeeding and a reduction in maternal dropout rates.</p> Conclusion <p>Application of counselling with the IMB model can motivate correct breastfeeding behaviours and improve maternal and infant health indices.</p> Trial registration <p>This trial is registered with the Iranian Registry of Clinical Trial with the identifier IRCT20170611034452N15 (registration date 20230428).</p>