We report structural and magnetic properties of spinel Co_3-xMn_xO₄ (x=0.1–1.0) synthesized by solid state reaction technique. Rietveld refinement analysis of X-ray diffraction (XRD) data, revealed the formation of polycrystalline single phase Co_3-xMn_xO₄ without any significant structural change in cubic crystal symmetry with Mn substitution, except change in lattice parameter. Temperature dependent magnetization data show changes in magnetic ordering temperature, indicating formation of antiferromagnetic (AFM) and ferromagnetic (FM) phase at low Mn concentration (x≤0.3) and well-defined FM phase at high Mn concentration (x≥0.5). The isothermal magnetization records established an AFM/FM mixed phase for composition ranging 0.1<x<0.5 and with strong FM phase above x>0.5.