The invention relates to a sound insulating structure including low-density and high-density layers. The low-density layer has first and second fibrous layers and ranges from 0.5 to 1.5 kg/m.sup.2 in surface density. The first and second fibrous layers are respectively made of first and second thermoplastic synthetic fibers. The first and second fibers respectively have first and second single fiber diameters, each of which diameters is in a range of from 3 to 40 .mu.m, and first and second fiber lengths, each of which lengths is in a range of from 10 to 100 mm. The high-density layer is formed on the low-density layer and is made of an air-impermeable polymer material and has a surface density that is higher than that of the low-density layer and ranges from 1 to 10 kg/m.sup.2. The low-density layer is high in sound-absorption coefficient and at the same time low in spring constant. Therefore, the sound insulating structure becomes substantially improved in sound insulating capability.