The invention relates to a process for preparing a powder formulation for inhalation for use in a dry powder inhaler, said powder comprising : (A) a carrier comprising : (a) 80 to 95 percent by weight, based on the total weight of said carrier, of coarse particles of a physiologically acceptable excipient having a mean particle size of at least 175 micron； and (b) 19.6 to 4.9 percent by weight, based on the total weight of said carrier, of micronized particles of a physiologically acceptable excipient, and (c) 0.1 to 0.4 percent by weight, based on the total weight of said carrier, of a salt of a fatty acid； and (B) micronized particles of glycopyrronium bromide, a long-acting O2 -agonist (LABA) and an inhaled corticosteroid (ICS), as active ingredients, said process comprising : (i) preparing by co-milling microparticles consisting of glycopyrronium bromide and a first part of an ICS in a ratio ranging from 80:20 to 70:30 by weight, wherein the volume diameter of said microparticles is not more than 15 micron； (ii) mixing the coarse particles of a physiologically acceptable excipient, the salt of a fatty acid, a first part of said micronized particles of a physiologically acceptable excipient, the micronized particles of said LABA, the co-milled microparticles obtained in step (i), and the remaining part of said ICS in a vessel of a shaker mixer at a speed of rotation not lower than 16 r.p.m. for a time of not less than 60 minutes, to obtain a first mixture； and (iii) adding the remaining part of the micronized particles of a physiologically acceptable excipient to said first mixture, to obtain a second mixture, and mixing said second mixture at a speed of rotation not lower than 16 rpm for a time of at least 120 minutes to obtain a formulation.
