The purpose of this study was to assess the role of Group Managed Grain Banks in ensuring rural food security. Specifically the study aimed to: describe the grain banks in terms of their functions and constraints, evaluate the contribution of grain banks on food supply consistency and security at household level and analyse operation performance of each grain bank. The study was carried in Dodoma region, using case study design at Kongwa and Chamwino districts. Purposive sampling was employed to select two villages in each district. A combination of qualitative and quantitative methods was used to collect data. Data were obtained from a sample of 100 respondents and processed by using Statistical Package for Social Sciences. Various analytical methods were employed. Descriptive analysis was used to describe socio-economic characters of respondents. T-test was employed to compare means of food security level between grain bank members and non members.Chi-square analysis of food security level across villages. Linear regression was used in establishing the relationship between indicators of food security level and predictor factors. Profit margin analysis was calculated for each grain bank to compare performances. The findings show that the main functions of grain banks are storage, food savings and food loan. Main constrains include poor management, inadequate capital and low compliance. Chi- square analysis shows that there is significant difference across villages. T-test result reveals that grain bank member households are more food secure than non member households, and statistically significant at 0.1 level of significance. Linear regression results shows that number of bags stored, total area cultivated and food loan access had direct bearing on food security status of the household. Profit margin ranged from 4.5% to 13.6% which imply a positive cash flow. It’s recommended that building capacity of grain bank in management skills be given high priority.