In this study, frequency optimization of symmetrically laminated folded composite plates is presented. The folded plates are modelled as a composite structure that consists of flat plates. The fundamental frequencies of one- and two-fold folded plates are maximized with respect to fibre orientations. The first-order shear deformation theory (FSDT) is used for vibration analysis of laminated folded plates. The modified feasible direction (MFD) method is used for the optimization routine. Therefore a program based on FORTRAN is used. Finally, the significant effects of length-to-thickness ratios, crank angles, different plate lengths and boundary conditions on the optimum results are demonstrated. (C) 2008 Elsevier Ltd. All rights reserved.