The growth of aluminum nitride films by reactive laser ablation has been studied. The influence of process parameters such as laser energy density, nitrogen pressure on the composition, chemical nature and structure of the films has been investigated. Rutherford backscattering spectrometry, nuclear reaction analysis, x-ray diffraction were used to characterize the films. The main problem in AlN film growth was the oxygen incorporation. The origin of this contamination and the mechanisms of incorporation were studied, and the crucial parameter was found to be the residual pressure during ablation. Due to the difference in chemical reactivity between oxygen and nitrogen atomic species, it is necessary to increase the density of atomic nitrogen to obtain pure AlN films. Thus, ar radio-frequency discharge device was added allowing a better nitrogen molecule dissociation. Finally, despite 10 percent O composition deviations, the AlN phase was obtained in the laser deposited films.