Abstract The paper presents the results of investigations concerning the application of zinc oxide - a wideband gap semiconductor in optical planar waveguide structures. ZnO is a promising semiconducting material thanks to its attractive optical properties. The investigations were focused on the determination of the technology of depositions and the annealing of ZnO layers concerning their optical properties. Special attention was paid to the determination of characteristics of the refractive index of ZnO layers and their coefficients of spectral transmission within the UV-VIS-NIR range. Besides that, also the mode characteristics and the attenuation coefficients of light in the obtained waveguide structures have been investigated. In the case of planar waveguides, in which the ZnO layers have not been annealed after their deposition, the values of the attenuation coefficient of light modes amount to a~ 30 dB/cm. The ZnO layers deposited on the heated substrate and annealed by rapid thermal annealing in an N₂ and O₂ atmosphere, are characterized by much lower values of the attenuation coefficients: a~ 3 dB/cm (TE0 and TM0 modes). The ZnO optical waveguides obtained according to our technology are characterized by the lowest values of the attenuation coefficients a encountered in world literature concerning the problem of optical waveguides based on ZnO. Studies have shown that ZnO layers elaborated by us can be used in integrated optic systems, waveguides, optical modulators and light sources.