Abstract: An aqueous dispersion of an aromatic polyethersulphone of sole repeat unit ##STR1## and having mean particle size below 25 .mu.m, preferably below 12 .mu.m, is prepared by (1) stirring the polyethersulphone in methylene chloride to form a solution and then a coarse particulate solid, (2) adding further methylene chloride to form a slurry, (3) milling the slurry to form a dispersion, (4) mixing a methylene chloride - and water-miscible liquid which does not swell the polyethersulphone with the milled dispersion, (5) filtering the dispersion and washing the wet cake with the liquid and then water, and (6) dispersing the wet cake in water, optionally with milling, to provide the aqueous dispersion.