We present a theoretical study of the electronic and excitonic states in InAs/GaAsSb quantum dots. We …rst center our study on the dependence of the antimony composition in the positioning of conduction-and valence-band alignments in InAs/GaAsSb/GaAs heterostructures. We predict a transition from type I to type II quantum dots at critical composition x c = 0:128, which describes well the experimental trend. We discuss the in ‡uence of the quantum dot size and antimony composition on the spatial distributions of carriers and the exciton binding energy. We …nd that the ground state exciton binding energy is always signi…cantly smaller (' 4 meV) for type II than for corresponding type I quantum dots (' 14 meV). Finally, we also predict the excitonic radiative lifetime and …nd 1 ns for type I and 10 ns for type II quantum dots, in agreement with the existing experimental literature.