摘要:Introduction. Nutritional status of lactating women is highly linked with the overall nutritional status of population. Undernutrition during lactation results in increased morbidity and mortality to the mother and her child. The literature is dearth regarding to nutrition status of lactating mothers in developing countries such as Ethiopia. Objective. The aim of this study was to assess undernutrition and associated factors among lactating mothers having child 6–23 months in Dega Damot Woreda, Northwest Ethiopia. Methods. A community-based cross-sectional study was conducted from March 21 to April 19, 2018. Simple random sampling technique was employed to recruit a total of 733 participants. Data were collected by using an interview-administered questionnaire and entered into EpiData version 4.2 and transferred to SPSS version 20 for further analysis. Factors associated with undernutrition were identified using multivariable logistic regression at a p value of less than 0.05 at 95% confidence interval. The direction and strength of association was interpreted using adjusted odds ratio. Results. In this study, the magnitude of undernutrition among lactating women was 21.8%. Being unmarried (AOR: 2.65, 95% CI: 1.54, 4.53), their first pregnancy <18 years (AOR: 2.34, 95% CI: 1.42, 3.87), having more than 5 number of pregnancies (AOR: 2.79, 95% CI: 1.55, 5.03), inadequate dietary diversity score (AOR: 2.1, 95% CI: 1.16, 3.83), and household food insecurity (AOR: 3.68, 95% CI: 2.35, 5.77) were significantly associated factors with undernutrition. Conclusions. The prevalence of undernutrition among lactating women was found to be high. Programs should do better in enhancing activities of agricultural production to reduce household food insecure and to increase accessibility of diversified diet. Other researchers better to do other studies to identify main factors of undernutrition using a qualitative study.