Co-authorship Recommendation is recommendation co-author which indicate have same interest. The way to find out the interest using the content such as abstract, list of citation and co-author of the researcher publication. This research proposed co-authorship recommendation by considering its context. The context is related the researcher interest. To collect the related context using ontology. The ontology used is CSO cause the dataset is in computer science domain. The ontology will expand the researcher interest, furthermore the recommendations will be expanded. There is no baseline in this dataset then the result of the process using clustering approaches. The previous method and the proposed method will be measured in Sillhouete Score. The proposed method surpasses the previous method. The proposed method SIL is 0.26% and the previous method SIL is 0.15% on the same dataset. Based on the evaluation measurement, ontology provides approaches affect for this recommendation. Ontology could expand the relevance of the terms which indicate another author with different interest but there is same interest in context