Background: The poor nutritional status of women has been a serious problem in Ethiopia for many years. Maternal dietary diversity is strongly linked to infants in the same household and to the average household nutrient adequacy. Hence, ensuring maternal dietary diversity to the acceptable level is very important in tackling malnutrition. Objective: To assess the dietary diversity, nutritional status and identify associated factors among lactating mothers visiting governmental health facilities of Dessie town, North Central Ethiopia from March to April 2017. Methods: Institution based cross - sectional study was conducted among 416 lactating mothers. Systematic random sampling technique was employed to select the study participants. The data were collected by using interviewer administered questionnaire and were entered into EPI-INFO, and analyzed using SPSS software. Bivariate and multivariate analyses were fitted to identify factors associated with the outcome variable and to test the strength of association. Results: The prevalence of underweight (BMI<18.5 kg/m2) among lactating mothers was 20.8%. The mean (±SD) dietary diversity score among the lactating mothers was 5.3 (±1.74) and more than half 227 (55.6%) of the study participants had inadequate dietary diversity. Inadequate women DDS [AOR = 3.5, 95 % CI (1.92, 6.28)] and household food insecurity [AOR = 2.6, 95 % CI (1.49, 4.38)] were factors associated with the under nutrition (BMI<18.5 kg/m2) of lactating mothers and household monthly income [AOR = 2.0, 95 % CI (1.15, 3.59)], type of house in which the mothers live [AOR = 1.9, 95 % CI (1.18, 2.95)], nutrition information [AOR = 1.7, 95 % CI (1.06, 2.58)] and household food insecurity [AOR = 1.7, 95 % CI (1.03, 2.96)] were factors associated with the dietary diversity of lactating mothers. Conclusion and Recommendations: Prevalence of underweight among lactating mothers was high. Nutritional factors were significantly associated with the under nutrition of lactating mothers. Socio-economic & demographic and nutritional factors were associated with the dietary diversity of lactating mothers. So, attention should be paid to food security and dietary diversity of lactating mothers to improve their dietary diversity and nutritional status.