The Semantic Web is an evolving development of the World Wide Web in which the meaning of information and services on the web is defined, making it possible for the web to understand and satisfy the requests of people and machines to use the web content. RDF and OWL is published by W3C for the standard of Semantic Web languages which can define relationships and structures between Web resources. Since the start of Semantic Web, the semantic web data is incrementally increased by Portal, Search Engines and Linking Open Data project. Therefore, the necessity of mining useful knowledge from huge size ontology is highly expected. However, the semantic web ontology has special characteristics to apply traditional decision tree algorithm which is the most popular in classification data mining. To overcome these problems, we proposed Semantic Decision Tree Algorithm which can perform on the semantic web ontology. This algorithm will help to mine the covered knowledge in the semantic web data.