Effect of bubble size on bubble-particle attachment and film drainage was studied based on the extended Derjaguin-Landau-Verwey-Overbeek theory and the Stefan-Reynolds flat film model. The disjoining pressure isotherms and wetting film drainage kinetics between a bubble and an model silica with different hydrophobic force decay lengths were calculated theoretically. It is found that the results depend on the shape's of total disjoining pressure isotherms. Film formed between a small bubble and silica surface always has faster drainage kinetics compared to that formed between a big bubble and silica surface due to the high Laplace pressure. For a monotonic repulsive total disjoining pressure, the wetting film is thermodynamically stable and the final equilibrium film thickness decreases with decreasing bubble size. In presence of a pressure barrier in total disjoining pressure, whether or not the film can rupture is determined by the magnitude between Laplace pressure and the pressure barrier. A small bubble is beneficial to the recovery of particles with weak and moderate floatability since the high Laplace pressure can drive the film to the range of hydrophobic force or even overcome the pressure barrier resulting in successful attachment. In flotation practice, much attention should be paid on bubble size since it not only affects collision efficiency but also influences the attachment behaviour. (C) 2017 Elsevier B.V. All rights reserved.