In an effort to develop an expert system for reservoir operations, a microcomputer-based system was built using knowledge concerning irrigation schedulings and practices for paddy rice. The system was tested its applicability based on the performance and the appropriateness using field data for Banweol district. The results of this study can be summarized as follows ; 1. A decision tree was constructed for irrigation reservoir operations and the knowledge base was built based on irrigation principles for paddy rice. 2. An expert system was developed from the knowledge bases using INSIGHT 2 which is a microcomputer-based, commercially available tool for expert systems, and uses the backward chaining as an inference engine. 3. The system performance was tested for different irrigation levels and ponded depths and the results seemed to be reasonable, implying that the knowledge base of the system is rightly constructed. 4. Cumulated reservoir release were generated from the system and compared with the historical records for Banweol reservoir. The results from the system were in good agreement with the field practices, and the squared root mean square values of 1986 and 1987 were 0.988 and 0.992, respectively. 5. This early version of the system should be used in a narrow scope due to its lack of the knowledge base, but it will be helpful to reservoir operation if the knowledge bases are extended to the advanced levels such as the prediction of inflow and irrigation amounts from rainfall forecasting.