In this thesis, structural, electrical and magnetoresistance properties of La 0.4 Pr 0.3 Ca 0.3 MnO 3 thin films have been studied.Thin films LPCMO are grown on LaAlO 3 (LAO)(111), SrTiO 3 (STO)(111), STO(110) and MgO (MGO)(100) substrates by pulsed laser deposition method . The effect of substrate type and films thickness on the structural and electrical properties of LPCMO thin films was considered during the deposition process. Thickness of thin films was determined by XRR method. Due to high compressive stress, the LPCMO sample on the LAO substrate with a thickness of 50 nm has high insulation behavior while it has a metal-insulation transition at 90 nm. The magnetoresistance of LPCMO/LAO film was 57%. The MGO substrate was used as a new substrate to investigate the effects of thickness on the electrical properties of thin films. The results showed that as the thickness decreased, the antiferromagnetic order of the insulator-charge is increased and the permeation between the metal ferromagnetic domains decreased. It was also observed at 50 nm thickness and at low transition temperatures of insulation-metal due to the coexistence of two phases of antiferromagnetic insulation and metallic ferromagnetism. The maximum anisotropic magnetoresistance (80%) was obtained in the LPCMO/MGO sample compared to LPCMO/LAO sample (32%). LPCMO / STO (110) sample had small different resistance in both directions of [1 0] and [001]. The effect of annealing on this sample resulted in anisotropic stress so that after annealing there was a significiant difference resistance between the two directions. After annealing, the sample showed good magnetoresistance (about 100%) and the anisotropic magnetoresistance decreased.