Thermo-optic coefficients (dn/dT) of inorganic-organic hybrid material films prepared by sol-gel process of organoalkylsilanes are measured using the prism coupler equipped with autocontrolled hot stage. In order to validate the reliability of this method, dn/dT of polymethylmethacrylate film is measured. dn/dT of inorganic-organic hybrid material films are negative and as high as the order of 10(-4), which are comparable to those of optical polymers. Their dn/dT increase with increasing organic content in the film and mainly depend on their thermal expansion. (C) 2002 American Institute of Physics.