Deep cement mixing and jet grouting is a widely adopted ground improvement method to solidify soft sediments. Several reports are available on the static strength and maximum shear modulus of cement-treated ground. This paper discusses the variation of shear modulus and damping ratio of cement-treated marine clay at various shear strain amplitudes. A series of resonant column tests and cyclic triaxial experiments are conducted to study the effects of effective confining pressure, curing stress, cement content, initial clay water content, and curing time on the shear modulus reduction and damping ratio of cement-treated marine clay. Results show that the maximum shear modulus increases by 88%, 131%, and 282% for clays treated with cement contents of 5%, 7.5%, and 10%, respectively, for 100 kPa confining pressure. For clay treated with 5% cement content and cured under 30 kPa stress, at a very small strain level, the shear modulus increases by about 37%, while the confining pressure increases from 100 to 200 kPa. However, the increase in shear modulus reduces to 7% for specimens cured under 90 kPa stress. However, the increase in shear modulus is more prominent at a smaller range of shear strains (<0.01%). Similarly, at 1% shear strain amplitude, samples cured for 28 days show 33% higher shear modulus than samples cured for 7 days. Conversely, the variation of the damping ratio with these factors seems negligible, especially at the small shear strain regime (<0.1%). © 2020 American Society of Civil Engineers.