Background: Physical activity behaviour during the postpartum period is very important to improve maternal health and prevent complications both in the short and long term. This study aims to evaluate the effect of a trans-theoretical model based intervention on physical exercises behaviour among postpartum women at Benha City, Egypt. Methods: A quasi-experimental design was utilized. The study was conducted at family planning outpatient clinic affiliated to Benha teaching hospital. A purposive sample of 86 postpartum women were included in the present study. Three tools were used for data collection; first tool: structured interviewing schedule to collect data about the subjects' demographic characteristics, medical and obstetric history and knowledge towards postpartum exercises. Second tool; the trans-theoretical model of behaviour change questionnaire, it composed of the four main dimensions that are stage of change, self-efficacy, decisional balance (pros and cons), experiential and behavioural process of change. Third tool; international physical activity questionnaire short-form to assess the postpartum physical activity level. Results: The mean age of the studied women was 28.88±5.89 years. There were statistically significant improvements (P<0.05) regarding to women' knowledge, and all constructs of trans-theoretical model which include self-efficacy, decisional balance, experiential and behavioural processes of change after the transtheoretical model based intervention as compared to before. Conclusion: The trans-theoretical based intervention was efficient in improving women's knowledge, postpartum exercise behaviour. This was observed in increasing women's self-efficacy, decisional balance pros, experimental and behavioural processes of change. While reducing decisional balance cons. Recommendation: The nurse should implement trans-theoretical model based interventions for postpartum women to promote postpartum exercise behaviour.