Semantic web ontology languages, such as OWL, have been widely used for knowledge representation. Through empirical analysis of real-world ontologies we discover that, like many natural and social phenomenon, the semantic web ontology is also "scale-free". Categories and Subject Descriptors D.2.8 [Software Engineering]: Metrics--complexity measures; I.2.4 [Knowledge Representation Formalisms and Methods]: Representation languages General Terms Measurement. Keywords Scale-free, Ontology, Semantic Web, Power-law.