By using an atomic force microscope, the influence of annealing on the surface topography of MgF2 films was studied. Hole growth and column coalescence were observed in the annealed films, and the coalescence process is very rapid. It was found that both the initial structure of the as-deposited films and the annealing temperature play important roles in the evolution of the surface topography of the thin films during the annealing process. The annealing process has a significant effect on the optical properties of the films.