Let KK be a field of characteristic zero, Xn={x1,…,xn}Xn={x1,…,xn} and Rn={r1,…,rn}Rn={r1,…,rn} be two sets of variables, LnLn be the free metabelian Leibniz algebra generated by XnXn, and K[Rn]K[Rn] be the commutative polynomial algebra generated by RnRn over the base field KK. Polynomials p(Xn)∈Lnp(Xn)∈Ln and q(Rn)∈K[Rn]q(Rn)∈K[Rn] are called symmetric if they satisfy p(xπ(1),…,xπ(n))=p(Xn)p(xπ(1),…,xπ(n))=p(Xn) and q(rπ(1),…,rπ(n))=q(Rn)q(rπ(1),…,rπ(n))=q(Rn), respectively, for all π∈Snπ∈Sn. The sets LSnnLSnn and K[Rn]SnK[Rn]Sn of symmetric polynomials are the SnSn-invariant subalgebras of LnLn and K[Rn]K[Rn], respectively. The Leibniz subalgebra (L′n)Sn=LSnn∩L′n in the commutator ideal L′n of Ln is a right K[Rn]Sn-module by the adjoint action. In this study, we provide a finite generating set for the right K[Rn]Sn-module (L′n)Sn. In particular, we give free generating sets for (L′2)S2 and (L′3)S3 as K[R2]S2-module and K[R3]S3-module, respectively.