Background: Maternal under nutrition is a worldwide public health problem affecting a high proportion of women in developing countries. Acute malnutrition is a major public health problem in Ethiopia and has significant impact on communities in particularly, the main health problems facing for pregnant women. Acute malnutrition in pregnancy increases the risk of gestational anemia, miscarriages, fetal deaths during pregnancy, pre-term delivery and maternal mortality. Objective: The aim of this study was to identify the determinants of acute malnutrition among pregnant women in Mekdella district , South Wollo zone, North East, Ethiopia, 2019. Methods: A Community based un matched Case control study design was conducted on 776 pregnant women in eleven kebeles of Mekdella district, South Wollo zone, Amhara region, from April to May 2019. The data was entered and cleaned using Epi data software version 3.1 then export to statistical package for social science version 20.0 for analysis. Binary logistic regression was used to identify the candidate variables and included in the multi variable binary logistic regression. The degree of association between independent and dependent variables were assessed using adjusted odds ratio and statistical significance was assessed a 5 % level of significance. Results: A total of 260 cases and 516 controls were included in the study with a response rate of 100% and 97.3% respectively. Pregnant women who were from food insecure households (AOR 2.2 [95% CI: 1.51 -3.12]), didn't get ANC visits (AOR 2.5 [95% CI: 1.71-3.55]), dietary diversity score less than or equal to three ( AOR 6.4 [ 95% CI: 4.39 -9.35] ), pregnant women who were from non- model households (AOR 1.8 [95% CI: 1.05-2.94]) and the odds of acute malnutrition among literate pregnant women were 0.65 less likely (AOR 0.65 [(0.44-0.96 ] ) lower than those who were illiterate were independent predictor of acute malnutrition. Conclusion: Pregnant women who didn't get antenatal care visits, low dietary diversity score, women who were from food insecure households, being non-model households were an independent predictor of acute malnutrition. Therefore provision of antennal care to all pregnant women is used as a point of entry for educating pregnant women and increase nutritional knowledge, attitude and counseling on consumption of diversify foods should be used as a main tool. Keywords: Determinants, acute malnutrition, pregnant women, Ethiopia