Let K be any unital commutative Q-algebra and z = (z 1 , ..., z n ) commutative or noncommutative free variables. Let t be a formal parameter which commutes with z and elements of K. We denote uniformly by K z and K[[t]] z the formal power series algebras of z over K and K[[t]], respectively. For any α ≥ 1, let D [α] z be the unital algebra generated by the differential operators of K z which increase the degree in z by at least α − 1 and Az , we introduce five sequences of differential operators of K z and show that their generating functions form a NCS (noncommutative symmetric) system ([Z4]) over the differential algebra D [α] z . Consequently, by the universal property of the NCS system formed by the generating functions of certain NCSFs (noncommutative symmetric functions) first introduced in [GKLLRT], we obtain a family of Hopf algebra homomorphisms S Ft :, which are also grading-preserving when F t satisfies certain conditions. Note that, the homomorphisms S Ft above can also be viewed as specializations of NCSFs by the differential operators of K z . Secondly, we show that, in both commutative and noncommutative cases, this family S Ft (with all n ≥ 1 and F t ∈ A[α] t z ) of differential operator specializations can distinguish any two different NCSFs. Some connections of the results above with the quasi-symmetric functions ([Ge], [MR], [S]) are also discussed.