In the context of deformation quantization, there exist various procedures to deal with the quantization of a reduced space M red . We shall be concerned here mainly with the classical Marsden-Weinstein reduction, assuming that we have a proper action of a Lie group G on a Poisson manifold M , with a moment map J for which zero is a regular value. For the quantization, we follow [6] (with a simplified approach) and build a star product ⋆ red on M red from a strongly invariant star product ⋆ on M . The new questions which are addressed in this paper concern the existence of natural * -involutions on the reduced quantum algebra and the representation theory for such a reduced * -algebra.We assume that ⋆ is Hermitian and we show that the choice of a formal series of smooth densities on the embedded coisotropic submanifold C = J −1 (0), with some equivariance property, defines a * -involution for ⋆ red on the reduced space. Looking into the question whether the corresponding * -involution is the complex conjugation (which is a * -involution in the Marsden-Weinstein context) yields a new notion of quantized unimodular class.We introduce a left (C ∞ (M ) [[λ]], ⋆)-submodule and a right (]-valued inner product and we establish that this gives a strong Morita equivalence bimodule between C ∞ (M red ) [[λ]] and the finite rank operators on C ∞ cf (C) [[λ]]. The crucial point is here to show the complete positivity of the inner product. We obtain a Rieffel induction functor from the strongly nondegenerate * -representations of (C ∞ (M red ) [[λ]], ⋆ red ) on pre-Hilbert right D-modules to those of (C ∞ (M ) [[λ]], ⋆) , for any auxiliary coefficient * -algebra D over [[λ]].