A study was conducted to assess the role of Water User Associations in the management of water use conflicts in Kilosa District, using a case of Ilonga River Sub-catchment. The specific objectives of the study were to characterize water resources and water users in the study area, to determine the level of conflicts among water users before and after the formulation of water user associations and to identify and assess the challenges and opportunities facing water user associations in water resource and water use conflicts management. The study used descriptive research design supplemented by the cross-sectional research design to achieve its objectives. Household survey through questionnaires and focus group discussions were used to collect data from three villages which were selected from the sub-catchment in such a way that the first village represented upstream users, and second village represented the midstream and the third village represented downstream users. The sample size was 120 representing 40 respondents from each village. A Statistical Package for Social Sciences software was used to analyze quantitative data while, inferential statistical analysis (t-test) was used to compare the level of conflicts before and after the formation of WUAs at Ilonga Sub-catchment. The results reveal that river water is the main source of water for agricultural production. The percentage of conflicts before the formation of WUA was found to be 22% but this fell to 4% after the formation of WUAs. This difference was found to be statistically significant (t=3.391, p=0.015). In order to reduce water use conflicts in the sub-catchment, solutions to conflicts among the farmers were identified. Among these is to ensure equitable water distribution among water users as it is considered to be the most effective solution in resolving water use conflicts in sub-catchment. The challenges facing water user associations include, climate change, water shortage, limited resources, and low community participation. Hence water management education is needed in order to design strategies towards sustainable water use and conflict management in the area.