(ZnSn)_1-xCu_xO nanocomposites (NCs) with nanorods and nanosheet morphologies were synthesized by a facile hydrothermal technique. (ZnSn)_1-xCu_xO NCs exhibited a gradual band gap redshift from UV to visible spectral region with increasing Cu-content. The room temperature magnetic hysteresis loop indicated the improvement of room temperature ferromagnetic (RTFM) behavior of (ZnSn)_1-xCu_xO NCs compared with nanostructured ZnSnO NCs induced by the exchange interaction of Cu-bound polarons with the localized spins and free carriers. The (ZnSn)₆₀Cu₄₀O NCs exhibited the highest saturation magnetization (M_s) of 0.539 emu·g⁻¹. Further increase in Cu-content resulted in the deterioration of crystalline domains and the reduction of M_s to 0.259 emu·g⁻¹. This behavior revealed that the electronic and magnetic properties of (ZnSn)_1-xCu_xO NCs were so sensitive to the dopant concentration that need to be utilized for improving their performance as good candidate NCs for spintronic applications.