Background: Acute malnutrition is a recent and severe weight loss as a result of acute food shortage and/or illness. It is the leading causes of morbidity and mortality of children aged 6-59 months as risk of death is nine times higher than that of children without it. In Ethiopia despite recent economic progress; nutritional status of children is among the worst in the world and it remains major public health problem. According to recently published mini demographic & health survey 2014; 9 % of children are wasted (3 % severely wasted) in the country and in Oromia region 8.8 % of children are wasted (1.7 % severely wasted). However there is no information on determinants of acute malnutrition in the study area. The aim of this study was to identify determinants of acute malnutrition among children aged 6-59 months in the study area. Methods: A facility based un-matched case control study was conducted on 339 (113 cases and 226 controls) children aged 6-59 months with their respective mothers from December 3, 2014 to March 25, 2015. The data were collected by using a pre-tested structured questionnaire and mid upper arm circumference (MUAC). Odds Ratio along with 95 % confidence interval was estimated to identify determinants of acute malnutrition (wasting) using the multivariable logistic regression. Level of statistical significance was declared at P < 0.05. Results: Wasting was associated with diarrheal diseases in the previous two weeks [AOR (95 % CI) =3.94 (2.01-7.73)], mothers habit of less frequent hand washing [AOR (95 % CI) =14.39 (7.33-28.22)], did not exclusively breastfed [AOR (95 % CI) = 2.63 (1.29-4.82)], having large family sizes [AOR (95 % CI) =2.59 (1.34-5.0)], absence of latrine [AOR (95 % CI) =2.99(1.23-7.06)], illiterate mothers [AOR (95 % CI) =2.16(1.14-4.11)] and febrile illness in the previous two weeks [AOR (95 % CI) =1.89 (1.0-3.59)].Conclusions: Wasting was significantly associated with diarrheal and febrile illness in the previous two weeks, lack of maternal education, hand washing & sub optimal breastfeeding practices, larger family size, and absence of latrine. Thus, an organized effort should be made at all levels to improve maternal and child health services, hand washing & breastfeeding practices, construction of latrines and education of mothers to restrain the problems of child acute malnutrition.