Abstract: In this study, an Object-Oriented (O-O) prototype Expert System (ES) for diagnosis of fungal diseases of date palm is presented. The objectives are to investigate, the potential of a proposed O-O model for expert systems and to provide intelligent computer-based support for farmers or agricultural specialists. The modeling of the system is based on O-O database and O-O rule base. An overview of the system's model and a description of its implementation are presented. The architecture of the ES resulted in a successful and flexible system that enhances soft computing and can also be used to develop expert systems for other domains.