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A kinetic Monte-Carlo simulation on magnetotransport behaviors of phase-separated magnetic conduction systems where the magnetic polaron aggregates are mixed with insulating phase is presented. The electron conductance is calculated by the spin-dependent electron tunneling among the magnetic polarons. The magnetotransport behavior as a function of volume fraction of magnetic polarons is simulated, reproducing the co-appearance of the insulating-metallic and ferromagnetic transitions. The metallic-insulating transition at low temperature is revealed. The picture of magnetic polaron aggregation as a mode magnetic insulator may be helpful to understand the magneto transport behaviors in manganites. (C) 2004 Elsevier B.V. All rights reserved.