The aim of the paper was to determine the influence of transverse shear deformation and rotatory inertia on the natural frequencies and on the values of displacements of beams made of fibrous composites reinforced with layers' of long fibres. It was assumed that the matrix of the composite beam possesses linear elastic and transversaIly isotropic properties. ; Moreover a reinforcement in the form of layers composed of long fibres symmetricaIly located in the cross section was considered. In order to describe the displacement and strain state of the matrix, Timoshenko theory was assumed. Using the complete analytical solutions obtained in the paper the accuracy analysis of results was performed in comparison with the theory of Bernoulli beam.