Microstructure, magnetic and electronic transport properties of the inhomogeneous system 1/m Ag2O-La0.833K0.167MnO3 (1/m is molar ratio, m=32, 16, 8, 4, and 2) have been studied. X-ray diffraction patterns show that all the samples are the two-phase composite and consist of a magnetic La0.833K0.167MnO3 (LKMO) perovskite phase and a nonmagnetic metal Ag phase. The room temperature magnetoresistance (MR) effect is enhanced significantly due to the addition of Ag. For the m = 4 sample the MR ratio increases from 10% of the pure compound LKMO to 32% under a lower field of 0.5 T and from ～35% of LKMO to 64 % under a higher field of 5.5 T at the temperature of 300 K. In the low temperature range from 4.2 K to 265 K, however, the MR ratio of the Ag-doped sample decreases with increasing the Ag content in the samples. The effect is discussed qualitatively by use of the relative change among the intrinsic MR effect and the extrinsic MR effect including the spin-polarized-tunneling and spin-dependent scattering effects at grain boundaries.