In this thesis the effect of Cu substitution and synthesis condition on the structural, magnetic and electrical properties of LaMn 1-x Cu x O 3 (0.00?x?0.125) manganite have been investigated. . The analysis of the XRD pattern showed that all samples except x=0.075 have orthorhombic structure with pnma space group and sample x=0.075 has rhombohedral structure with ace group. The structural parameters and space groups have been obtained by FullProf software, Rietveld refinement.The AC magnetic susceptibility measurements showed that, the curie temperature increased with increasing the Cu content until x=0.075 and then, decreased in x=0.125. This means that, the double exchange interaction becomes weak with high Cu doping and increases in low Cu doping. All doped samples, in low temperature showed a drop in the real part and a peak in imaginary part of AC magnetic susceptibility curves. The peak is related to spin glass state in the samples. The AC susceptibility depends on the frequency and field. Fitting with conventional critical slowing down model demonstrates that samples are the spin glass at low temperatures. According to the electrical resistivity measurements, the increasing of the substitution content till x=0.075 results in decreasing of electrical resistivity and increasing of electrical resistivity at higher level of doping. Fitting of electrical resistivity plots with small polaron hoping (SPH) and variable range hoping (VRH) models demonstrates the nice agreement by the SPH model. Kay words: manganite, spin glass, AC susceptibility, sintering, doping, Super exchange, double exchange.