The thickness dependence of strain and magnetic properties of La0.8Ca0.2MnO3 (LCMO) thin films grown on SrTiO3 (STO) substrates were investigated by X-ray diffraction techniques and magnetic measurements. The results show that all the LCMO films are well oriented in the (00l) direction on the (001) STO substrate. The LCMO thin films have a pseudo-cubic structure. With the film thickness increasing, the in-plane lattice parameters decrease while the out-of-plane lattice parameter increases. The lattice parameter a is close to b, but a little smaller than c. The in-plane strain in the film is tensile due to the lattice mismatch between the LCMO film and STO substrate, whereas that out-of-plane is compressive. The LCMO films have a slightly perceptible mosaic structure along the qz direction, and there exists an angular deviation of about 0.1° between ［001］LCMO and ［001］STO. The physical properties of the films strongly depend on the film thickness. With the increase of the film thickness the TMI is enhanced, and the MR is weakened.