A series of tests were conducted to investigate the improvement of damping properties of clay samples with geosynthetic inclusions. Flexible thermoplastic polymer synthetics improve damping properties of clay samples. Resonant column tests were conducted to measure the low strain shear modulus and damping ratio of laboratory prepared synthetic inclusion clay specimens. The shear modulus and damping ratio of the reinforced clay samples were investigated considering geosynthetic type (geotextile and geomembrane), number of geosynthetic sheets, and confining pressure. The test results demonstrated that the geomembrane and the number of geosynthetic sheets significantly improved the shear modulus and damping ratio of reinforced clay samples compared with those of the unreinforced clay samples.