ZnO∶In thin films with thickness varying in the 210—240nm range were prepared on quartz substrates by sol_gel spin_coating technique. The structural properties of these thin films (In/Zn=0, 1, 2, 3 and 5at%) were studied by grazing incidence X_ray diffraction, conventional X_ray diffraction, Fourier transform infrared spectroscopy, atomic force microscopy and photoluminescence. It is found that the ZnO∶In thin films are composed of the unstressed bulk layer packed up by large grains with (002) plane and the surface layer by small grains with (002) and (103) planes, and a proper In doping concentration can improve structural properties of ZnO thin films. The analytic results were further proved by grazing incidence X_ray diffraction at different incidence angles (α=1, 2, 3 and 5°).