This study suggests the method of converting thesauri to SKOS step by step and it is formalized in three stages of the conversion process. The study develops output and guidelines for each stage. The converting stages are: (1) Collecting and analyzing thesauri for understanding about structure of terms and semantics of relation. (2) Defining the conversion method and creating ontology of the thesauri. (3) Examining the preservation of forms and various semantic relations between the thesauri and then creating SKOS ontology. This method can be applied to the thesauruses with complicated relations in concepts. In the future, it is needed to have an embodiment of conversion after making the algorithm of conversion by stage with the method suggested in this research.