We optimized the deposition conditions of polycrystalline nanoporousGaN coatings produced by Chemical Vapor Deposition on Si substrates, by exploring the effect produced by the Ga holder shape, the initial amount of Ga, the reaction deposition time and the metallic catalyst used. Such polycrystalline films probed to act as antireflective coatings by reducing the reflectance of Si substrates by 50% or more, and that of flat GaN samples by 40% in the UV and 83% in the visible, at the same time that they exhibit an almost constant reflectance from 400 to 800 nm, important to develop UV sensors with enhanced sensitivity. Furthermore, the polycrystalline nanoporous coatings we developed exhibit hydrophobic behaviour, with a static contact angle of 119°, and a contact angle hysteresis of 4.5°, which might contribute to enlarge the durability of such functional films, by the self cleaning effect induced.