In this paper, the sensitivity of the LiNbO3 surface acoustic wave (SAW) based humidity sensors has been enhanced with various nanostructured Ag materials, including thermally evaporated or chemically synthesized, and then thermally annealed ones. The results showed that the humidity sensitivity of the SAW devices increases with the surface roughness (porosity) of the sensing film, and can be further improved when Ag NPs are used. Smooth Ag film deposited by evaporation onto the SAW devices did not change the humidity sensitivity noticeably, but those with chemically deposited high porosity Ag films have a good sensitivity of 80 kHz/75%RH. The SAW sensors with the Ag NPs have the highest sensitivity up to about 800 kHz/75%RH, at least one order of magnitude higher than those reported before. The SAW sensors with Ag nano-particles showed a strong non-linearity, and explained by the different chemisorption capabilities of Ag and LiNbO3 surface.