The thermo-optic coefficient (dn∕dT) of porous silicon has been measured. The measurements are based on a simple technique. The experimental data, in the wavelength range between 500 and 1100nm and at different porosities, have been compared with the Bruggeman and Landau–Lifshitz models. The results show good agreement in case of the Bruggeman model for porosities lower than 0.7, while for higher porosities the Landau model is in better agreement. An estimation of dn∕dT as a function of the porosity at the fiber optic communication wavelength of 1.55μm has also been reported.