The reaction between hydrogen atoms and an ultrathin aluminum film (2 monolayer) on a Mo(111) substrate was studied by thermal desorption (TD) and Auger electron spectroscopy (AES). Through TD experiments for the hydrogen precovered aluminum films, desorption of aluminum hydride was observed at 370 K. It was confirmed that 1/3 monolayer of aluminum was desorbed as aluminum hydrides after a TD experiment for the aluminum film on which hydrogen was preadsorbed to a full monolayer coverage. The aluminum film was continuously etched at 410 K by a steady flow of hydrogen atoms. These results indicate the potential capability of hydrogen atoms as a selective etchant for aluminum.