Background: Under-nutrition is the most known significant public health problems in developing countries of the world including Ethiopia that cause a shocking effect on children under five years of age. However, the extent of the problem and its several risk factors were not uniformly addressed enough across the various corner of the country. Thus, the objective of this study was to estimate the extent of under-nutritional status and to identify factors related to under-nutrition among children aged 6-59 months in Gida Ayana district, West Ethiopia. Method: A community based cross sectional study was conducted in August/September, 2015. A total of 588 children aged 6-59 months with their respective mothers/caregivers/were used for this study. Weight, height and Mid- upper Arm Circumference (MUAC) were measured using instruments that are recommended by UNICEF (United Nations Children’s Fund) and data regarding socioeconomic, demographic, child and maternal characteristics were collected using a pretested structured questionnaire through interview. Statistical Package for Social Sciences (SPSS) software version 20.0 was used to perform descriptive statistics as well as to perform bivariate and multivariate logistic regression analysis to identify factors related to under-nutritional status of children. World Health Organization (WHO) Anthro 2007 software version 1.0.4 was used to analyze anthropometric indices. Results: The overall prevalence of stunting, wasting, and underweight were 40.5%, 10.9% and 19.2% respectively. In addition, prevalence of severe stunting; wasting and underweight were 13.4%, 2.9% and 4.6% respectively. Wasting was significantly higher in male children, 24-35 months aged children, House Holds (HHs) of illiterate fathers and HHs with lack of access to safe drinking water. Stunting were significantly higher in male children, children aged 36-59 months, HHs with lack of ownership of farm animals, children with diarrhea, children with fever and HHs with low monthly income. In addition, male children, urban children, children aged 24 months and above, HHs having more than one under five children and diarrhea were the factors that showed significant association with underweight. Conclusion: The prevalence of wasting and stunting among under five children were high confirming nutritional situation in the study area is serious. Wasting, stunting and underweight were significantly higher among boys than girls. In addition; child age, residence, parent’s formal education status, visiting antenatal clinic, and diarrhea becomes the main risk factors that contribute for the occurrence of at least two forms of under-nutritional status of children in the study area. Thus, efforts should be made to improve sources of drinking water and parental education, to prevent and control childhood illness, to implement child’s age, residence and sex specific interventions as well as to establish therapeutic and supplementary feeding programs.