Impurity effects on the stability of a charge-ordered antiferromagnetic state in La0.4Ca0.6MnO3 are investigated by Fe3+/Cr3+ doping on Mn-site. All the samples with different doping concentrations possess the same orthorhombic crystalline structure,and no evident variation in the structure can be seen. Our results reveal that the Fe3+/Cr3+ doping effects on the transport behavior are rather different, although both impurities have the same valance and are commonly antiferromagnetically coupled with other transition metal ions. We assign this remarkable different doping effects to the different electronic structure of the doping cations.