Nutrition is a fundamental pillar of human life and its requirement varies with respect to age, gender and during physiological changes such as pregnancy. The aim of this study was to assess the knowledge of pregnant mothers on maternal nutrition and associated factors in Guto Gida Woreda, East Wollega Zone, Ethiopia during January to June of the year 2013, and using quantitative cross-sectional descriptive study on a sample of 422 pregnant women and supplemented by qualitative study (focus group discussion). The quantitative data were analyzed using SPSS for windows version (16.0). Multiple logistic regression was run to assess factors that were associated with the dependent variable at p<0.05 and to control the confounders. This research showed only 64.4% of women had nutrition knowledge during pregnancy. There was a positive significant relation between information about nutrition, educational status of mothers and family income and nutrition knowledge of mothers during pregnancy (p<0.001). The knowledge of pregnant mothers was relatively low in this study. Information about nutrition, family income and educational status of mothers had a positive significant relation with mothers’ nutrition knowledge in the study area. Hence, the government in collaboration with concerned bodies should focus on nutritional education and information about nutrition to increase the knowledge of pregnant mothers on nutrition and put in practice during pregnancy in the study area.