Reservoirs are built usually to serve multiple purposes, viz. irrigation, municipal and industrial water supply, hydro-power and flood control. Because of high variability of annual rainfall and conflicting demands on scarce water resources, the study and operation of reservoir systems has assumed great significance to meet the short and long-term requirements. The reservoir managers do not find previous techniques of complex optimization models are difficult to adopt practically. New methods have to be developed, which are simple to understand and can be effectively adopted for the existing systems. Artificial intelligent tools like Genetic programming, Neural Networks and fuzzy logic methods are increasingly becoming popular in Water resources applications. The fuzzy-rule-based systems are very much suitable for inferring developed operating policies. In the present work a rule-based Fuzzy model is attempted for long-term operation a multi-reservoir system. The model was developed on monthly basis for operation and the model was demonstrated with a case of two serial reservoirs on River Godavari sub-system located in South India. The uniqueness of the present paper is that the model was developed based on the historical operation so that the model may be acceptable to reservoir managers, since the departmental expertise was the basis for the model development. The performance of the model was tested with both calibrated and validation periods. The performance of model during two crop seasons of year was reported. © 2006 by World Scientific Publishing Co. Pte. Ltd. All rights reserved.