Material properties of polymer composite reinforced by glass fibers were deter-mined by a numerical-experimental method. The method is based on the use of experimental data of the natural frequencies and vibration modes of the speci-mens, methods for their experimental determination, a finite element model for computational modal analysis, and a procedure for solving the identification prob-lem. The identification problem of the parameters of composite material model is considered as a problem of minimizing the discrepancy between the experimental and calculated values of natural frequencies. To solve it, the random search meth-od was used. The vibration modes and natural frequencies of the experimental specimens were determined by scanning laser vibrometry. The goal of the work is to estimate the accuracy of the numerical-experimental method for identifying the mechanical properties of composite materials based on experimental data of natural frequencies and vibration modes of specimens in the form of plates and beams. The evaluation of the error in determining the elastic characteristics was performed on two specimens of laminated fiberglass with the same number of layers and layups. Using the parameters of the composite material determined, the numerical and experimental values of the natural frequencies of the plate and beam were compared. Despite the 18% difference of the identified values of the elastic moduli of the beam and plate specimens, the distinction between the exper-imental and numerical values of their natural frequencies did not exceed 6%.