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The free vibration analysis of stiffened laminated composite plates has been performed usingthe layered (zigzag) finite element method based on the first order shear deformation theory. The layers ofthe laminated plate is modeled using nine-node isoparametric degenerated flat shell element. The stiffenersare modeled as three-node isoparametric beam elements based on Timoshenko beam theory. Bilinear in-plane displacement constraints are used to maintain the inter-layer continuity. A special lumping techniqueis used in deriving the lumped mass matrices. The natural frequencies are extracted using the subspaceiteration method. Numerical results are presented for unstiffened laminated plates, stiffened isotropicplates, stiffened symmetric angle-ply laminates, stiffened skew-symmetric angle-ply laminates andstiffened skew-symmetric cross-ply laminates. The effects of fiber orientations (ply angles), number oflayers, stiffener depths and degrees of orthotropy are examined.