Abstract-In this paper we intends to build an expert system based on semantic web for online search using XML, to help users to find the desired software, and read about its features and specifications. The expert system saves user's time and effort of web searching or buying software from available libraries. Building online search expert system is ideal for capturing support knowledge to produce interactive on-line systems that provide searching details, situation-specific advice exactly like setting a session with an expert. Any person can access this interactive system from his web browser and get some questions answer in addition to precise advice which was provided by an expert. The system can provide some troubleshooting diagnose, find the right products; … Etc.The proposed system further combines aspects of three research topics (Semantic Web, Expert System and XML). Semantic web Ontology will be considered as a set of directed graphs where each node represents an item and the edges denote a term which is related to another term. Organizations can now optimize their most valuable expert knowledge through powerful interactive Web-enabled knowledge automation expert system. Online sessions emulate a conversation with a human expert asking focused questions and producing customized recommendations and advice. Hence, the main powerful point of the proposed expert system is that the skills of any domain expert will be available to everyone.