Undoped and fluorine-doped ZnO thin films deposited by spray pyrolysis onto soda-lime glass substrates were electrically and optically characterized. Resistivities as low as 1 x 10(-1) Omega cm, Hall mobility as high as IO cm(2)/V per s and effective carrier concentration as high as 4 x 10(19) cm(-3) have been obtained. Relative fluorine concentration was determined by the resonant nuclear reaction method. Electron concentrations due to the fluorine incorporation as an effective electrically active donor is always lower than fluorine contents on the films and in the starting solution. Average optical transmisttance on the whole visible range as high as 92% (substrate losses not included) have been obtained for the best conductive films. The refractive index of layers was found to increase with fluorine doping and substrate temperature. The fluorine incorporation, at ZnO thin firms, results in a band gap widening effect,