The structure, electronic and magnetic properties of perovskite (1 − x)La_0.7Ca_0.3MnO₃(LCMO)/xCu (x is a mass percentage, x = 1%, 3%, 5%, 7%, 9%, 15%, 20%) have been studied. The nano-scale metal Cu powder was doped into the LCMO matrix. The results showed that some Cu element substituted for Mn ion in LCMO and the remainder resided in the grain boundaries in the form of a CuO phase because of the oxidation process when the Cu powder was sintered at high temperature in air. Cu existed in the form of Cu³⁺ ions in the samples at a low doping level (x ≤ 3%) and Cu²⁺ ions appeared when x > 3%. Because of the larger ionic radius of Cu²⁺ ions compared with the average Mn radius, it is likely that the Cu²⁺ ions in the proximity of the grain boundaries tend to separate into the boundaries. An amorphous phase of the Cu element was formed in the grain boundaries, which respond to the unusual electrical and magnetic behaviours of the heavily doped samples. A maximum MR value (~50%) around 210 K was observed in a magnetic field of 3000 Oe for the 5% doped samples. Besides the effect of Cu substituting for Mn ions in LCMO, the MR behaviour is also attributed to the properties of dopants which reside in the grain boundaries of the matrix grains.