Epitaxial FePt thin films with various thicknesses, having in-plane uniaxial magnetic anisotropy, have been prepared at different deposition temperatures using sputtering technique. L10 ordering in the FePt thin film leads to very large uniaxial magnetocrystalline anisotropy. The magnetocrystalline anisotropy energy increases with the increase in film thickness and deposition temperature. Domain imaging performed by Magneto-optic Kerr microscopy with a longitudinal geometry suggests that the domain structure and magnetization reversal process strongly depend on the film thickness and the deposition temperature. For the films deposited at a certain temperature, there exists a critical thickness where the coercive and saturation fields show maxima.