Papaya is one of the fruits commodity that grow in the plateau and lowlands. It makes papaya vulnerable to pests and diseases that impedes optimal yields. In this study, an expert sistem was build that was able to store a knowledge base for the diagnosis of pests and diseases of papaya plants. A method of information retrieval is needed that the knowledge base becomes dynamic. Forward Chaining is a method of finding knowledge that starts with existing information and combines rules to produce a conclusion. The Best First Search technique is used for fact finding to obtain optimal results. Forward Chaining method that was build in expert sistems allow the sistem to perform the simple searching result on the database facts. The knowledge was obtained from experts. Web-based expert sistem has 6 pest data and 7 disease data, 41 pest and disease symptom data, and also 12 treatment techniques. Fifty data of papaya trees that had been sustained by disease were used in the test. The test results showed a sistem accuracy is 96% compared to experts.