In this study, in-land water cycle model for Lake Victoria basin is proposed and the long-term water balance is estimated under future meteorological condition using this model and GCM products provided by CMIP5 in this basin. Proposed in-land water cycle model is composed of four modules: land-surface(SiBUC), river routing, dam operation, and irrigation. Proposed hydrological model concluded available water resources and discharge from the Lake increase, though, water level keeps almost same level as the present one. On the other hand, the results from each GCM show too much different trend.This study makes it clear that it had better to discuss on usage of water resources in this basin under future meteorological condition considering the risks of both of flood and drought.