Abstract: Classical ontology supported by formalized concepts is unable to represent the imprecision and uncertainty information. Ontology incorporated with fuzzy logic is a solution to the problem. Considering the difficulty to generate the fuzzy ontology in accordance to pre-defined concepts, framing the fuzzy ontology on the basis of fuzzy conceptual model is proposed. The UML conceptual model and OWL DL ontology are therefore fuzzily extended separately on the basis of fuzzy set theory, and the feasibility of framing the fuzzy OWL DL ontology by fuzzy UML class diagram is interpreted in the perspective of their logical foundation. Then, the formalized mapping transformation of fuzzy UML class diagram into fuzzy OWL DL ontology is studied to show the mapping rules and axiomatization process. Framing the fuzzy OWL DL ontology with existing fuzzy conceptual model can reduce efficiently the complexity of framing the fuzzy ontology and, meanwhile, enhance the expressibility of ontology.