In this paper, the influence of carbon nanotubes on vibrational properties of laminated composite plates is studied theoretically and experimentally. The plates are made of glass/epoxy composite. Multi walled and single walled carbon nanotubes in different weight percentages are added to these composites. At first, carbon nanotubes are dispersed in the epoxy resin via ultrasonic procedure. Then the composite plates are made by hand layup and vacuum bagging methods in a mould manufactured for this research. Mechanical properties of the fiber composite reinforced by carbon nanotubes calculated using modified Halphin-Tsai equations. Next composite plates are modeled in ABAQUS software and frequency analysis is done. Also vibrational properties of structure are obtained by experimental modal analysis in fixed boundary condition. Experimental results showed 210% increase in damping for samples which have 0.5 weight percent of single walled carbon nanotubes (in comparison with plane glass/epoxy composite plates). Also a good agreement was observed between obtained natural frequencies from finite element analyses and experimental tests.