Undernutrition continues to be a major cause of high infant and below five years children mortality in Tanzania. This study was carried out to find out factors influencing nutritional status of under five year's children in Mbarali district. Nutritional assessment was done by using of anthropometric measurements which were subsequently compared to WHO criterion (SD classification) using summary indices of nutritional status: weight-for-age, height-for-age and weight-for-height and MUAC. Overall one hundred sixty (160) children aged below five years were included in the study. Socio-economic, health, environment sanitation and food availability factors were also assessed. Chi-square test was used to detect association between variables which could affect nutritional status of a child. Results showed a total of 39.4% of children were underweight out of whom13.8% were severely underweight. Wasted children were 27.5%, among them 5% were severely wasted. Prevalence of stunting was 30.7%, out of whom 5% were severely stunted. Based on sex of the child 2.5% female were stunted and male were 3.1%. Mid Upper Arm Circumference by sex showed that 1.8% female were severely undernourished, while 3.1% male children were severely undernourished. The study also explored relationship between socio- economic factors (age, occupation, education of the mother and family size) with nutritional status. Statistical analysis showed no significance though mothers with informal and primary education had more children with severely stunted children (5%) compared to secondary school leavers. Other factors that influenced nutritional status were found to be birth weight, diseases, type of food storage, and weaning age of the children. The study concluded that under nutrition is still a problem in the area. Awareness on age ofiii introducing food to children, frequency of feeding, education against low birth weight, public encouragement on good practice of personal hygiene and proper environment sanitation practices should be conducted to families and community members to reduce the problem.Gender Unit in the President's Office- Public Service Management,