The aim of this study was to evaluate the effect of an intensive dry coating process on the improvement in flow behaviours for fine cohesive lactose powders as a function of size distribution and coating process parameters. Various commercial fine lactose powders with particle size range from approximately 4 to 120 mu m were dry coated with magnesium stearate using a recently optimised mechanofusion approach. The bulk densities for all cohesive powders increased and flow behaviours were improved substantially except for the already free-flowing powder of R010 (with VMD approximately 120 mu m). Of particular note, the originally non-flowing cohesive powder P450 with VMD approximately 20 mu m achieved free-flowing characteristics and was as flowable as R010 after mechanofusion. The improvement in powder flow behaviours was shown to be dependent on coating parameters such as coating speed and coating time duration. At an appropriate coating speed, optimal coating can be achieved after processing for 5 min for P450. This study demonstrated that an optimised mechanofusion process is an efficient and effective approach for substantially improving flow of fine cohesive powders to achieve equivalent flow behaviours of much larger sized powders. (C) 2010 Elsevier B.V. All rights reserved.