In this paper we present the logic F P (Ł n , Ł) which allows to reason about the probability of fuzzy events formalized by means of the notion of state in a MV-algebra. This logic is defined starting from a basic idea exposed by Hájek [Metamathematics of Fuzzy Logic, Kluwer, Dordrecht, 1998]. Two kinds of semantics have been introduced, namely the class of weak and strong probabilistic models. The main result of this paper is a completeness theorem for the logic F P (Ł n , Ł) w.r.t. both weak and strong models. We also present two extensions of F P (Ł n , Ł): the first one is the logic F P (Ł n , RP L), obtained by expanding the F P (Ł n , Ł)-language with truth-constants for the rationals in [0, 1], while the second extension is the logic F CP (Ł n , Ł 1 2 ) allowing to reason about conditional states.