Laser melting and re-solidification has been used to density and homogenize ceramic surfaces, leading to increased high temperature corrosion and erosion resistance. Although complete sealing of pores can be achieved on the surface, pores have been observed in the boundary between the laser treated zone and the untreated bulk. This paper investigates the mechanisms of pore formation and the various factors affecting it. Theoretical models describing the final boundary porosity and pore size, including pore coalescence, are presented. The models show that pore formation is strongly dependent on laser beam energy density, but the determining factor is porosity and pore size distribution prior to laser treatment. The theoretical models are compared with experimental results based on the laser surface treatment of alumina-based refractory ceramics. The general morphological features of the porosity at the untreated bulk/treated zone boundary are in good agreement with the model predictions. (C) 2002 Elsevier Science B.V. All rights reserved.