Introduction: Undernutrition among children is a major public health problem in developing countries including Ethiopia. Undernutrition among children is a critical problem because its effects are long lasting and go beyond childhood. Objective: Todetermine the prevalence of undernutrition status and its associated factors among children 6-59 months of age in Gilgel Beles town, North West Ethiopia, 2019. Methods:A community-basedcross-sectional study was conducted on 422 study participants. Systematicrandom sampling technique was used to select samplingKebeles and study units. Weight and height were measured using calibrated instruments. The data were entered into SPSS and calculated using SPSS version 20.0 statistical software and/or WHO Anthro2007 softwarewith aid of Stat/Transfer.Bivariable and multivariable logistic regression analysis methods were used to identify determinants of undernutrition and to account for potential confounding factors. Results:Overall prevalence of undernutrition was 54.5% and the levels of stunting,wasting, and underweight were 51.2%, 4.4%, and 16.1%,respectively. Associated factors with undernutrition;age of mother when she gave birth (AOR=2.612,95%CI:1.647-4.144), number of child under five in HH (AOR=0.357,95%CI:0.217-0.587), exclusive breast feeding (AOR=0.538,95%CI:0.332-0.870),birthweightstatus in gram (AOR=2.870,95%CI:1.065-7.732), occupation of mother (AOR=3.4885,95%CI:1.494-8.125 and AOR=1.868,95%CI:1.060-3.294) and fever (AOR=1.752,95%CI:1.017-3.018). Conclusion:Undernutrition was high in Gilgel Beles town among children under five yearsof age.Numberof child under five in HH, Exclusive breast feeding and Age of the children in months were controle factors, but Age of mother when she gave birth, ,Birth weight status, Occupation of mother and Childhood illness indicated by feverwere risk factors affecting under five undernutrition in Gilgel Beles town. Recommendation:Should be taken aserious measure to end premature marriages in the area, shouldbe arranged childcare centers for mothers who are nursing in public institutions, should improve health facilities met by qualified health professionals, should improve nutritional education and exclusive breast feeding practices in the study area. Researchers explore further factors related with the undernutrition, qualitative studies need to be conducted in study area