A ceramic sample of Pb₂Sr₂Y_0.5Ca_0.5Cu₃Oy containing no impurity phases was prepared by reacting PbO and Sr-Y-Ca-Cu-0 precursor in a flowing nitrogen gas at 750-C. Powder X-ray diffraction pattern shows that it has an orthorhombic structure with lattice parameters a=0.537nm, b=0.542nm and c=1.576nm. The samples which have various oxygen contents(y) ranging from 8 up to neary 10 were prepared by oxidation of this material. The relation between oxygen contents and superconducting properties was investigated by electrical resistivity measurement using a DC four-probe technique. The sharpest superconducting transition among these samples was observed on a slightly oxidized material. The samples with large oxygen content which have tetragonal structure show semiconducting behavior.