Pure, single-phase La0.7Ca0.3MnO3 perovskites with giant magnetoresistance effect have been successfully prepared by mechanical alloying. The amorphous phase formed in milled smples transforms at about 920K into perovskite-type phase. Following the law of mass action, crystallization dynamics of the amorphous phase has been discussed. The activation energy for crystallization transformation is calculated to be about 265kJ/mol. The characterization of resistivity ρ(T) for La0.7Ca0.3MnO3 perovskites has also been investigated. At low temperatures T, ρ(T) has a directproportion dependence on T2. With increasing annealing temperature, the slope of ρ-T2 curve decreases. The temperature dependent magnetoresistance effect at temperatures far below the Curie temperature can be well expressed by the equation Δρ/ρ0=p1-p2T3/2-p3T5/2.