The vibratory properties of fibreglass reinforced unsaturated polyester plastic were studied by the low frequency vibrating method. In this study, the fibreglass weight contents of FRP were 0%, 10%, 20%, and 30% respectively, and the directions of the FRP plates were flow direction, 45$^{circ}$ bias direction and perpendicular to the flow direction. The results obtained were as follows: 1. The dispersed fibreglass reinforced plastic shows anisotropic itv in dynamic modulus due to the fibre orientation in the molding. 2. The results of the comparison between the theoretical and experimental moduli were out of accord with each other. 3. The relationship between the dynamic modulus and the volume fraction of fibreglass was almost linear only when the direction of the FRP plate was in flow direction.