Tin oxide thin films were deposited at 375 T on a-alumina substrate by metal-organic chemical vapor deposition (MOCVD) process. A number of hillocks on the film were formed after air annealing at 500 T for 30 min and few things in N-2 annealing. The oxygen content and the binding energy after air annealing came to close the stoichiometric SnO2. The cauliflower hillocks of the film seem to be formed by the continuous migration of crystallites from a cauliflower grain on the substrate to release the stress due to the increase of oxygen content and volume.