Abstract: To realize the semantic similarity estimation for Formal Concept Analysis (FCA) concepts or concept lattices, the formal contexts of FCA are extended into semantic cases by using the concepts of Description Logics (DLs) to act as the attributes of formal contexts, that is, a kind of semantic representation for formal contexts is presented using domain ontologies (DL knowledge bases). Furthermore, a framework for semantic similarity estimation of FCA concepts and concept lattices by using DL reasoning (i.e., ontology reasoning) is proposed based on the semantic representation for formal contexts. The framework ensures that the semantic similarity measures resulting from instantiations fulfill fundamental properties such as symmetry and equivalence invariance.