The lactating mothers in developing countries like Ethiopia are the first targeted and nutritionally vulnerable groups to under nutrition due to different socio demographic factors which influence the health and well being of mothers and children. During lactation periods, mothers need more nutritious food than the rests of the household members. The aim of this study was to determine the nutritional status, associated factors and dietary diversity of lactating mothers 15-49 years old in Offa woreda. A crosssectional community based study was carried out to determine the Chronic Energy deficiency of lactating mothers in the studied woreda. The lactating mothers were randomly selected from four rural and two urban kebeles. A total of 422 households were visited and the required data were collected as scheduled in all selected kebeles. The prevalence of under nutrition among the lactating mothers in the studied area was determined using BMI by Anthropometric measurements and the blood sample test for hemoglobin (Hb) concentration was done using Haemocue methods. The collected data were analyzed using Stata version 14.2 software. Among the participated lactating mothers the values 15.8%, 74.2%, 8.3% and 1.7% were obtained for under weight, normal, over weight and obese in their BMI (kg/m2), respectively. The studied participants of 15.8% were in chronic energy deficiency according to WHO guidelines. The lactating mothers' percentage value 36.4%, 59.3%, 4.3% were in age group of 15-24, 25-34 and 35-49 years, respectively. The blood test showed that among the lactating mothers 11.4% were found anemic which had got hemoglobin level less than normal level (12g/dl). The daily dietary diversity intake per day of lactating mothers was classified as high (>5 DDS) 1.2%, medium (4-5 DDS) 50.7% and low (<3 DDS) 47.4% among the nine food groups recommended for women dietary diversity score (WDDS). The independent variables: education, family size, marital status and occupation were significantly associated with nutritional status of the lactating mothers at P<0.05. In conclusion the majority of the lactating women in the study area had normal BMI. The researchers would like to recommend that the government and development agencies should focus on the risk factors identified, to ensure better health and nutrition for lactating mothers in this woreda.