Background: Maternal chronic energy deficiency remains a persistent problem and an important contributor to morbidity, mortality and poor birth outcomes in developing countries. Despite this, there is scarcity of data on the burden of maternal chronic energy deficiency (under nutrition) and associated factors in Ethiopia and particularly in the study area. Objective: The aim of this study was to assess the chronic energy deficiency and associated factors among lactating mothers under two years’ old children Method: A community based a cross-sectional study Supplemented on 599 currently lactating woman less than two years old children in Simada District. Study participants were selected using multi -stage sampling technique considering 1.5 design effects. Data were collected using semi structured interviewer administered questionnaire. The data were collected by six health extension workers and three supervisors who had first degree in nursing. Before the data collection pretest was done on 5% of sample. Data were edited and entered into Epi data version 4.4 and cleaned and analyzed using SPSS for windows version 23.Bivariate and multiple logistic regression were compute. Odds ratios and their 95% confidence interval were computed to determine level of significance. Statistical significance was declared at P values less than 0.05. Result: The magnitude of chronic energy deficiency was found to be 34.1 %( 30-38.2%, 95%CI). Multivariable logistic regression analyses showed that having additional meal during breast feeding was protective [(AOR=0.219, 95%CI :( 0.114, 0.422), p woman who had three and more under-five children [(AOR=5.026, 95%CI :( 2.755, 9.169), p ,Women who had not nutrition education [(AOR=24.319, 95%CI: 9.980, 59256), p , woman who did not have minimum and [(AOR=8.500 95%CI: 3.117, 23.179), p ] were more likely experience chronic energy deficiency. Conclusion: The prevalence of chronic energy deficiency among lactating women was found to be 34.1 %( 30-38.2%, 95%CI). Number of under five children in the household, attending nutrition education, additional meal during breast feeding and minimum dietary diversity status of study subject were significant predictors if chronic energy deficiency. Recommendation: nutrition promotion messages are needed to focus to improve diversification of food, additional meals during breast feeding, minimum dietary diversity.