To provide a water-based vibration-damping composition exhibiting vibration-damping performance over a wide range of temperatures, and yielding coating film with high elongation at break at low temperatures and high breaking strength at high temperatures and low specific gravity.

The water-based vibration-damping composition comprises a water-swelling synthetic inorganic phyllosilicate having an mean particle size of ≥3μm and a hydrophobic resin aqueous dispersion where a hydrophobic resin with a glass transition temperature of ≤0°C is dispersed in an aqueous medium so as to be ≤0.5μm in mean particle size. In this composition, the amount of the water-swelling synthetic inorganic phyllosilicate is 1-30 pts. mass based on 100 pts. mass of the hydrophobic resin.