La0.7Ca0.3MnO3 thin films with various thicknesses were successfully fabricated on SrTiO3 single crystal substrates via sol-gel method. X-Ray diffraction manifests that all the films have highly preferential orientation. Electrical transport measurement shows a strong impact of film thickness on the physical properties of La0.7Ca0.3MnO3 thin films, which can be attributed to the change of lattice structure of the films substrate induced by strain. Further study indicates that in the films with small film thicknesses, variable range hopping of small polarons is the dominant transport process at high temperatures, and in those films with larger thicknesses small polarons are the predominant charge carriers even at very low temperatures.