The Si3N4/FePt/Si3N4/Al/Si structures have been fabricated. 57 nm silicon nitride films have been used as dielectric layer for heat dissipation and 500 nm Al film used for reflection layer. The Kerr rotation angle was changed with the FePt layer thickness. At the 65 % Pt composition in 10 nm FePt layer, the maximum Kerr rotation angle was 0.82°. As increase with FePt thickness the Kerr angle is slightly decreased. The change of Kerr rotation angle and the thermal behavior of multilayered structure according to FePt thickness variation were also calculated by computer simulation.