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A series of Cd1-xCuxCr2S4 (x=0.01, 0.04, 0.1, and 0.2) ceramics have been prepared by a solid state reaction method. The X-ray diffraction patterns suggest that the samples have a cubic spinel phase with a space group Fd3m and a tiny amount of Cr2O3 impurity phase. X-ray photoemission spectroscopy reveals a bivalence of Cu and trivalence of Cr in Cd0.8Cu0.2Cr2S4. The replacement of Cd by Cu leads to a slight shift of magnetic transition temperature TC. The saturation magnetic moment per formula unit at 2 K and effective moments in paramagnetic region decrease with Cu content, which is attributed to the coexistence of low spin state Cr3+ with S=1/2 and high spin state Cr3+ with S=3/2 as deduced from the M-H and M-T measurements. The transport measurements suggest that the Cu2+ doping enhances the carrier density. In contrast, a significant decrease in magnetoresistance is observed upon Cu doping. The magnetoresistance effect is discussed based on the magnetic polaron theory.