The In-substituted system,(La2/3Ca1/3)(Mn(3-2x)/3In2x/3)O3(x=0.00，0.10，0.15),was synthesized by solid-state reaction method.Its temperature dependence of electrical resistance and magnetoresistance (H=0,1.6T) and field dependence of magnetoresistance were measured by the four-probe method.It was found that when x increases,both the peak of the electrical resistivity and the peak of magnetoresistance move to lower temperatures.However,the cusp is broadened by In-substitution.The authors suggested that the variation of the proportion of In3+ ions leads to the change of manganese valence and the magnetic moments,as well as magnetic structure of the (La2/3Ca1/3)(Mn(3-2x)/3In2x/3)O3 system.Such phenomena weaken the ferromagnetic double exchange effect.