Background Nutrition asserts to be a fundamental for child growth and development. Undernutrition increases the risk of child morbidity and mortality becomes a major public health challenges in developing countries. The aim of study was to assess prevalence of stunting, wasting and underweight among children aged 6-23 months in Dalit and Non-Dalit and associated factors.Method A cross sectional comparative study was conducted among mothers with their children aged 6-23months in Dhanusha district. Overall, 599 respondents were taken through multistage simple random sampling of which 300 from Non-Dalit and 299 from Dalit. Anthropometry measurement and interview were used for data collection technique and structure questionnaire was applied as a tool. Using Statistical Package for the Social Science, descriptive and inferential analysis were done.Results Prevalence of stunting, underweight and wasting were 49.9%, 34.8% and 13.4% in Dalit and 39.0%, 25.0% and 8.7% in Non-Dalit respectively. Stunting was significantly associated with family type (AOR=1.93, 95% CI: 1.11-3.34) among Dalit while age of child (AOR=0.24, 95% CI: 0.10-0.57), ante natal care visit (AOR=3.20, 95% CI: 1.15-8.90) and media exposure (AOR=3.10, 95% CI: 1.11-8.64 in Non-Dalit. The underweight were significantly associated with age of child(AOR=0.50; 95% of CI: 0.27-0.93), knowledge on child feeding (AOR=2.00; 95% of CI: 1.13-3.54) and media exposure (AOR=1.78; 95% of CI: 1.01-3.14) in Dalit while media exposure (AOR=2.45; 95% of CI: 1.23-4.89) and duration of food sufficiency (AOR=2.51; 95% of CI: 1.10-5.71) in Non-Dalit. The wasting were significantly associated with minimum meal frequency (AOR=2.48; 95% of CI: 1.04-5.93) in Dalit while birth interval (AOR=0.27; 95% of CI: 0.08-0.92) in Non-Dalit.Conclusion Prevalence of undernutrition got high in both groups. Family type in Dalit and age of child, knowledge on child feeding and media exposure in Non-Dalit were key factors of stunting. Age of child, knowledge on child feeding and media exposure in Dalit while media exposure and duration of food sufficiency were important factors of underweight. Minimum meal frequency in Dalit whereas birth interval in Non-Dalit were the major factors of wasting. Community based nutrition education, food security and health service utilization programme should help in reduction of undernutrition.