Two kinds of composites of La0.67Ca0.33MnO3/ZrO2 and La0.67Ca0.33MnO3/YSZ have been investigated, in which the heterogeneous oxide YSZ represents yttria-stabilized zirconia (8 mol% Y2O3 + 92 mol% ZrO2). Their transport properties are measured in a temperature range of 10-300 K and a magnetic field range of 0-3 T. With increase in ZrO2 doping level for the range of 0-2%, the metal-insulator transition temperature, T-P, decreases, but T-P increases with the doping level increase further for higher than 2%. Meanwhile, in the composite of La0.67Ca0.33MnO3/ZrO2, besides the intrinsic metal-insulator (ferromagnetic-paramagnetic) transition, a new kink and a widen transition temperature region are observed both in the temperature dependence of resistivity and magnetization curves. Compared to pure La0.67Ca0.33MnO3 and the composite of La0.67Ca0.33MnO3/YSZ, we assume that the different effects between ZrO2 and YSZ on transport behavior of La0.67Ca0.33MnO3 result mainly from their different chemical stability. (C) 2003 Elsevier Ltd. All rights reserved.