Background: the second stage of labor (time from cervical dilatation of 10 cm to delivery of the fetus) is often the most stressful part of the childbearing process for the woman and fetus, and consequently for the health care provider. duration of the second stage of labor is influenced by many factors. Therefore, this study aimed to determine the duration of the second stage of labor and associated factors among mothers who gave birth in health facilities of Bahir Dar City, Northwest Ethiopia. rnMethods: prospective cohort study was conducted among 283 mothers who gave birth in selected health facilities of Bahir Dar city from September to December 2019. Data were collected using face to face interviews, document review and anthropometric measurement techniques. the data were entered into EPI DATA version 3.1 and exported to STATA version 12 for analysis. Both descriptive (frequencies, percentages and median time for second stage labor) and analytic statistics (Cox regression analysis) were performed. The proportional hazard assumption test was done using the Schonefeld residual.rnResult: overall median duration of the second stage of labor was found to be 40.9 minutes (27.7 minutes in multi-parous mothers and 49.5 minutes in nulliparous mothers).proportion of the prolonged second stage of labor was 28.83 % (95%, CI;16-31,) in nulliparous mothers and 15.5 %( 95%, CI; 9-19) in multi-parous mothers. Lack of physical activity, inadequacy of uterine contraction, occipito-posterior fetal position, and birth weight of greater than 4000 grams, and Inadequacy of maternal pelvis, were predictors of prolonged second stage of labor.rnConclusion: The proportion of prolonged second stage of labor was higher in nulliparous than multi-parous mothers. Lack of Physical activity, inadequacy of uterine contraction, occipito-posterior fetal position, and birth weight of greater than 4000 grams, and inadequacy of maternal pelvis were predictors of the prolonged second stage of labor.