Lactating mothers from low-income countries including Ethiopia are considered as a nutritionally vulnerable group due to different socio demographic factors which impact on the health and wellbeing of children. Adequate nutrition for the mothers during lactation is therefore important for their good health as well as for that of their offspring. We aimed to assess nutritional status, and associated factors among lactating mothers in Nekemte Hospital and Health Centers, East Wollega, Ethiopia. Institutional based cross-sectional study was conducted from January 2014 to June 2014. Body Mass index was used to measure the nutritional status by measuring height and weight of the lactating mothers using standard procedures. Data on socio-demographic characteristics, maternal nutritional status, and associated factorswas collected from all lactating mothers who visited both health institutions during postnatal care and EPI program. The association of nutritional status with socioeconomic and demographic factorswere analyzed using descriptive statistics, binary and multiple logistic regression analysis. This study revealed that majority of the women 260(81.3%) was in the age range of 17-25 yrs and attending school 292 (91.3%). The prevalence of underweight, normal, overweight and Obesity were 65(20%), 240(75%), 20(4.7%) and (0.3%), respectively. From multiple logistic regression analysis family size (AOR=4.604, 95%CI=1.903-11.140 andfamily income (AOR=0.250, 95%CI=0.100-0.623) were significantly associated with the nutritional status of the study participants. Nutritional statuses of the lactating mothers were short of the national and international recommendations. Therefore, sustained nutrition education is recommended to the lactating mothers and their families and communities to improve food intake, proper dietary knowledge during lactation in order to enhance health and nutrition outcomes of lactating mothers and their children. Proper family planning and the way that lactating mothers increase their income should be designed by concerned body.