A new modified antireflective coating was prepared by base catalyzed sol–gel process using tetraethylorthosilicate as precursor and polyvinyl butyral as modifier. The properties of the silica sols and AR coatings were characterized with Fourier-transfer infrared absorption spectroscopy, particle size analyzer, transmission electron microscope, programmable rheometer, UV–Vis spectrophotometry, ellipsometry, atomic force microscope and contact angle measurement. It was found that addition of 4% PVB greatly enhanced moisture-resistance of the AR coating. Optical transmittance of 4% PVB modified AR coating on BK7 substrate was found to be nearly 100%. The water contact angles of normal and 4% PVB modified AR coating were 51 and 53°, respectively, which indicates no significant increase of hydrophobicity of the modified coating. The peak transmittance of 4% PVB modified AR coating was almost unaffected after being exposed to the moist surroundings while that of normal silica coating decreased sharply from 99.8 to 96.5% within 2 weeks. The excellent moisture-resistance of PVB modified AR coating may be attributed to the adsorption of PVB on the surface of AR coating.