Magnetic inhomogeneity in colossal magnetoresitive lanthanum manganites and its effect on MR properties are reported. Polycrystalline bulk specimens of La0.67Ca0.33MnO3 were prepared by solid state reaction and sol-gel route. By controlling materials processing parameters, CMR specimens with different magnetic quality (M-0 = 91-93 emu g(-1), T-c = 240-270 K) were obtained. The MR properties of these specimens were characterized to be a broad, rather than a sharp as in a typical CMR materials, transition of semiconductor to metal and multiple peaks in MR versus T curve, which was explained by the co-existence of several La1-xCaxMnO3 phases with different magnetic transition temperature (T-c). The extent of inhomogeneity was in coincidence with the magnetic quality of the specimens. The magnetic inhomogeneity was found to severely degrade a field sensitivity at the temperature where the peak MR ratio was observed. The presence of paramagnetic secondary phase at the temperature was proposed to explain the degradation of field sensitivity.