Background: Weight gain is a biological phenomenon that supports the functions of the growth and development of the fetus. Women who do not gain enough weight during pregnancy have a risk of bearing a baby with low birth weight. Inadequate weight gain in pregnancy is low in developed countries while still common in some developing countries, including Ethiopia. Although inadequate weight gain is common, data regarding to its burden is very scarce. No study has been done about gestational weight gain in Bahir Dar city. So it needs localized based study. Objective: To assess gestational weight gain and associated factors among mothers attending labor at the selected health facility in Bahir Dar City, Northwest, Ethiopia, 2022. Methods: A facility-based cross-sectional study design was conducted from May 2022 to July 2022 among 821 study participants who were selected using a systematic random sampling method. Data was collected by interviewer-administered questionnaire and chart view among mothers attending labor. Data were entered by EPI data version 3.1 and exported to SPSS version 23 for analysis. A binary logistic regression model was fitted to identify factors associated with inadequate weight gain during pregnancy. Level of significance was declared at P-value<0.05 with its 95% CI. Texts and tables were used to present the data Result: The study revealed that 63.2 %( 95%CI; 59.30, 66) of the women gained inadequate gestational weight. The factors associated with inadequate gestational weight gain were poor knowledge on weight gain (AOR= 1.45; 95%CI; 1.07, 1.95), gestational age less than 37 weeks (AOR=1.44;95% CI;1.08,1,92)and food consumption Lessthan three times a day (AOR=1.35;95% CI; 1.00, 1.81) . Conclusion and recommendation: In this study most of pregnant women gain inadequate gestational weight. Early pregnancy body mass index, knowledge about weight gain, frequency of food consumption and gestational age were significantly associated with inadequate weight gain. Enhancing counseling and health education for pregnant mothers during ANC visit is so important to reduce inadequate weight gain.