Work-related musculoskeletal disorders (WMSDs) significantly challenge female assembly line workers due to repetitive tasks, manual force, poor posture, and static muscle contractions. Increased ergonomic preventive behaviors through learning-by-doing (LBD) approach could probably be essential to mitigate these issues. This study investigates the impact of a structured, theory-based educational intervention using the learning-by-doing approach to promote ergonomic behaviors and decease MSDs subsequently. This randomized controlled trial (RCT) conducted in 2023 investigated the effectiveness of a theory-based ergonomic training program among Iranian women working on electronics assembly lines. Participants were randomly assigned to an intervention group, which received a structured training program based on Social Cognitive Theory (SCT), or to a control group with no intervention. Outcomes were assessed using the Ergonomic Behavior Evaluation Tool (EBET) and the Nordic Musculoskeletal Questionnaire (NMQ) at baseline and at 3, 12, and 24 weeks post-intervention. A total of 80 women participated in the trial, with an average age of 37.87 ± 5.15 years in the experimental group and 37.10 ± 6.81 years in the control group. Although both groups were the same at initial time of the study, there was a significant difference between the two groups in the average scores of all theoretical constructs at 3, 12, and 24 weeks after the intervention, except for the outcome expectancy construct, which was not significant at 24 weeks post-intervention. The experimental group demonstrated a significant improvement in performing ergonomic behaviors compared to the control group. Additionally, women in the experimental group reported a significant reduction in pain in some areas of their bodies. Based on the effect of the educational intervention through LBD approach on and the ergonomic behaviors, it emphasized to apply this training among assembly line workers. however, to further reduce musculoskeletal pain, it is recommended to incorporate other dimensions of ergonomic interventions, supported by macro management levels at the industry level. ClinicalTrials.gov IRCT20220825055792N1. Registered on 23 September 2022 with the IRCTID.