We report theoretical results on the structure, static, and dynamic polarizability of hydrated nitrate anion in finite size cluster, NO3-·nH 2 O (n=1–8) based on the first principles electronic structure methods. The interesting observation is that for 3⩽n⩽8, the surface structures are more stable than the corresponding interior structures. It is observed that the polarizability (both static and dynamic) varies linearly with the size (n) of the hydrated cluster. It is found that the dynamic polarizability becomes infinite at a frequency of 6.12eV. This observation is in very good agreement with the previously measured electronic transition energy corresponding to 6.13eV for nitrate anion in aqueous solution.