Chitosan microparticles cross-linked by tri-polyphosphate (TPP) anions have been prepared by spray drying. Two different cross-linking methods have been employed ex-situ cross-linking whereby aqueous solution of cross-linked chitosan nanoparticles has been spray-dried by a two-fluid nozzle, and a novel in-situ crosslinking method, whereby solutions of chitosan and TPP have been fed to a three-fluid nozzle and crosslinking occurred within individual droplets. The size and morphology of the resulting microparticles have been characterised and their dependence on the cross-linking ratio and the initial chitosan concentration determined. Particles produced by the three-fluid nozzle were found to have favourable properties in terms of stability in aqueous media and they allow the use of higher chitosan concentrations, which makes them suitable for microencapsulation applications. (C) 2012 Elsevier B.V. All rights reserved.