The L1 0 FePt alloy has been extensively studied and proposed as a promising candidate for ultrahigh density recording media. Due to its large magnetocrystalline anisotropy and very small crytical grain size, FePt becomese thermally stable at room temperature, In this research we have investigated the effect of substrate temperature, lattice mismatch and Ta capping layer and underlayer on the structure and magnetic properti es of FePt thin films.In all samples, the external magnetic field have been used to improve and control the intensity of Laser plume. FePt thin films were prepared by pulsed laser deposition on Si(100) and Si/SiO 2 (100) single crystal substrates at different substrate temperatures of 600 , 700 and 800 ° C , under ultrahigh vacuum 3.3× 10 -6 Torr. The microstructures, degree of ordering, surface morphology and magnetic properties of FePt thin films were investigated. The results showed that L1 0 crystal structure was created. As the temperature increased, the growth of grain size was observed. The increasing of stress from due to the lattice mismatch in FePt/Si (100) thin film leads to change of surface morphology from Island- like mode to continuous mode. Also, the roughness of surface and coercivity increased with increasing lattice mismatch and temperature. Results indicated that the strain from the lower lattice mismatch improved the ordering of the FePt films. also in this research we used Ta for capping layer and underlayer in FePt thin films with quartz substrate. In this part, FePt thin films were deposited onto quartz substrate at room temperature.The layer structure was Ta/FePt/Ta/Quartz. the samples were then subjected to rapid thermal annealing (RTA) at temperature of 500 , 700 and 800 ° C for 30 min with heating rate of about 60 ° C/s In these samples, The results of Xray diffraction patterns showed that the L1 0 crystal structure was not created. The very low coercivity were obtained for these samples.