The effects of titanium content on the optical and mechanical properties of silica-titania hard, optical films by the sol-gel technique using gamma-glycidoxypropyltrimethoxysilane, methyltrimethoxysilane, and tetrapropylorthotitanate as starting materials are studied. Thermal gravimetric analysis, ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, and Raman spectroscopy are used to investigate the optical and structural properties of the films. The results indicate that crack-free and high transparency silica-titania film with a thickness more than 0.6 mum can be obtained by a single spin-coating process after a heat treatment at 500 degreesC. The hardness and Young's modulus of the films are characterized by a nanoindenter and they show a linear dependence on titanium content. Hardness as high as 6.60 GPa is obtained in a 0.5 M titanium content film and heat treated at 800 degreesC. It is proposed that the high hardness of the film may be related to the carbon and titanium content in the film. (C) 2003 American Vacuum Society.