Let b ≥ 2 be a positive integer. Let D be a finite subset of Z and {n k } ∞ k=1 ⊆ N be a sequence of strictly increasing numbers. A Moran measure μ b,D,{nk } is a Borel probability measure generated by the Moran iterated function system (Moran IFS)In this paper we study one of the basic problems in Fourier analysis associated with μ b,D,{nk } . More precisely, we give some conditions under which the measure μ b,D,{nk } is a spectral measure, i.e., there exists a discrete subset Λ ⊆ R such that E(Λ) = {e 2πiλx : λ ∈ Λ} is an orthonormal basis for L 2 (μ b,D,{nk } ).