The magnetic and electrical properties of La0.67Sr0.33MnO3 ( LSMO ) are influenced very much by the Nb dopant. However, this doping effect is restricted by the limited Nb solution into LSMO due to the low calcined temperature. As a result, a second phase LaNbO4 appears in our samples. Enhancements of the low-field magnetoresistance (LFMR) were observed both at 77 K and room temperature in the manganite system prepared by doping Nb2O5 into LSMO powders. The doping amount x of Nb ions ranges from 0-10 % molar ratio. The MR ratios at 77 K with H = 1 T and H = 0.1 T are 33.8 % and 24 % for the x = 0.07 doped sample, respectively. A MR effect up to 9 % was also found for the sample with x = 0.05 at room temperature, which is 2.2 times as large as that for LSMO (4.1%). The spin dependent tunneling and scattering at the interfaces of the grain boundaries are responsible for the LFMR while the high field magnetoresistance (HFMR) originates from the spin dependent transport related to noncollinear spin structure at the interfaces.