Provided is a composition for a sound insulating sheet member, a sound insulating sheet member, and a sound insulating structure body with excellent sound insulating performance. A sound insulating structure body including: a plurality of convex-shaped rubber-elastic resonant portions; and a sheet-like support that supports the resonant portions, wherein the resonant portions have a storage modulus G′ obtained from a composite curve of dynamic viscoelasticity according to ISO 6721-4 of 100 MPa or less at 25° C. and 10 kHz, and the areal density of the support is 1.0 kg/m2 or less.