Background Newborn survival is a prominent goal on the global health agenda and an important area of focus for programs seeking to ensure child survival. Geographically, neonatal deaths are most prevalent in Sub-Saharan Africa and southern Asia, accounting for 39% and 38% of all neonatal deaths respectively while Ethiopia in particular has 28% neonatal death. Promotion of essential newborn care practice is one of a cheap approach to improve health outcomes of newborn babies. Thus, this study was aimed to assess the magnitude of essential newborn care practices and associated factors among postnatal mothers in Nekemte city, Western Ethiopia. Methods An institution-based cross-sectional study was conducted from February to March, 2017, in Nekemte city, East Wollega Zone. Data was collected from 417 randomly selected mothers who have less than six months infants by face to face interview in three public health institutions of Nekemte City, Ethiopia. Women who were not biological mother to the newborn were excluded from the study. The collected data were coded, cleaned and entered using Epi-Data version 3.1 and analysed using Statistical Package for Social Science (SPSS) version 21.0. Both bivariable and multivariable logistic regression analysis were computed to identify associated factors. The strength of association was measured by odds ratios with 95% confidence interval (CI) at a p-value of < 0.05 and finally obtained results were presented by using simple frequency tables, graphs, and charts. Results The study revealed that the level of essential newborn care practice was 184(44.1%). The overall safe cord care practice of the respondents was 285 (68.3%) while the optimal thermal care practices and good neonatal feeding were 328 (78.7%) and 322 (77.2%) respectively. Having visit to Antenatal Care (ANC) [Adjusted Odds Ratio (AOR) = 4.38, 95% CI =