We present RAT-OWL, a software system for reasoning about typicality in preferential Description Logics. It is implemented in the form of a Prot ́eg ́e 4.3 Plugin and it allows the user to reason in a nonmonotonic extension of Description Logics based on the notion of “rational closure”. This logic extends standard Description Logics in order to express “typical” properties, that can be directly specified by means of a typicality operator T: a TBox can contain inclusions of the form T(C) v D to represent that “typical Cs are also Ds”. We show experimental results, indicating that the performances of RAT-OWL are promising