A series of sodium metal silicate solid solutions, Na₂Mg_1-xZn_xSiO₄ (x = 0–1.0) has been successfully synthesized through high temperature solid state reactions. While the space group of a model compound, Na₂MgSiO₄ is Pna2₁ (Orthorhombic), Na₂ZnSiO₄ crystallizes in Pn (Monoclinic). Na₂MSiO₄ (M = Mg, Zn) consists of SiO₄, MO₄ tetrahedral and sodium cations. The two original compounds reveal similar structures and both materials are crystallizing in noncentrosymmetric space groups. Furthermore, the solid solutions, Na₂M_1-xZn_xSiO₄ (x = 0.2, 0.4, 0.6, 0.8), crystallize in either Pna2₁ or Pn. The crystal structures of the reported solid solutions were determined by powder X-ray diffraction. Phase transition depending on the amount of transition metal cations has been studied by the diffraction method. In addition, the effect of polarization of d¹⁰ transition metal cations on the second-harmonic generation properties of the solid solutions has been also examined.