Abstarct: In this thesis, undoped and doped SnO2 thin films with different percentages of Co and Fe were synthesized on glass and Si substrates by Sol-gel method. The effects of Fe and Co doping, annealing temperature, thickness of laxyer and substrate on structural, optical, magnetic and electrical properties of the films were investigated. XRD, AGFM, optical transparency measurements and FESEM images were used for samples characterization . SnO2 films with %10 Co doping were synthesized and the samples were annealed at 300, 400 and 500⁰C. XRD analysis of samples showed that the crystal orientation changes with increase in annealing temperature and the best annealing temperature was chosen to be 400⁰C. The XRD patterns of the samples doped with different percentages of Co, show the cubic structure with (111) preferred orientation. Optical transparency decreased with increase in doping and FESEM images showed that grain size decreases with increase in Co percentage. Increasing the films thickness caused cubic structure changes into rutile tetragonal structure and the optical transparency and the band gap decreases. Annealed samples on Si substrate at 400, 550⁰C displayed (111) preferred orientation. The XRD spectra of the films with 0, 10, 30 of Co on Si substrate indicated that this films have rutile tetragonal structure but at %20 doping, cubic structure was observed. Grain size decreased with increase in Co doping. Undoped and Fe doped SnO2 films on glass substrate with percentages of 20 and 30 had cubic structure but %10 doping showed rutile tetragonal Structure. Optical transparency and band gap decreases with increase in doping. The magnetic measurements of the doped SnO2 samples with percentages 10,20 of Co were carried out but ferromagnetic property has not been observed at room temperature.