Abstract: Polycrystalline La_1-xSr_xMnO_z thin films with (202) preferred orientation were successfully synthesized on amorphous quartz substrates by metal-organic decomposition (MOD). Porous structure in the films was revealed by atomic force microscope. Good linearity of magnetotransport property and about 5% magnetoresistance (MR) ratio under 10 kOe field are obtained at room temperature. A large MR ratio of about 11% under 2 kOe field is observed at 77 K, showing an obvious low-field MR effect. The temperature dependence of resistance presents a smooth metal-insulator transition far below the magnetic transition, and the MR monotonically increases with decreasing temperature under 8 kOe field, both of which are related to the structural defects in the films including grain boundaries and porosity.