Аннотация:The laser excitation has been used to register the ionization and fluorescence spectra of rare-earth (RE) monoxides molecules in natural gas - air flame. The mechanisms of RE monoxides molecules ionization in a flame have been studied. It has been shown that the collisional ionization dominates for the scandium monoxide molecules. In the case of the yttrium monoxide the photo-ionization contribution is also significant.