Thin films of zinc oxide were deposited on glass by r.f. sputtering and studied by means of spectrophotometry and spectroscopic ellipsometry. We first reviewed the methods used to determine simultaneously the microstructure and optical indices of thin films. These methods have then been used to analyze the experimental measurements. They clearly showed that the microstructure of thin films could only be determined by using spectroscopic ellipsometry measurements. From these measurements, the optical indices of the zinc oxide films in the wavelength range 310-750 nm were then computed. These correlate closely with previously published results.