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The La2/3Ca1/3Mn1-xCuxO3(x=0.04)samples with different grain size were prepared by sol-gel method. The x-ray diffraction proves that all the samples are single phase and Cu doping and different sintering temperature do not change the lattice structure. Resistance versus temperature shows that semiconductor-metal transition moves to low temperature along with grain size decreasing. The experiment show that intergrain magnetoresistance increase from 25% to 51% in 25 K and 0.4 T as grain size decrease. The result of experiment indicates that intergrain magnetoresistance effects are substantially improved by lower level Cu doping in La2/3Ca1/3MnO3 polycrystals synthesized at low temperature and by minimizing grain size.