We have studied the difference in the thermoelectric properties of CU₂ZnSnSe₄ and CU₂Zn_0.5Cd_0.5SnSe₄. The samples were prepared using solid state synthesis method. The x-ray diffraction analysis revealed the formation of the phases. The temperature dependence of thermopower, electrical resistivity and power factor were measured for both CU₂ZnSnSe₄ and CU₂Zn_0.5Cd_0.5SnSe₄. The difference in the properties can be attributed to the fact that substitution of Zn by Cd causes an alteration in the electrical insulating path by the larger Cd atom. The electrical resistivity increases by several orders of magnitude in CU₂Zn_0.5Cd_0.5SnSe₄. Since the Seebeck coefficient is high for CU₂ZnSnSe₄, five times increase in power factor was seen in comparison to CU₂ZnSnSe₄ and CU₂Zn_0.5Cd_0.5SnSe₄