A process for preparing a dry powder formulation for use in a dry powder inhaler, said formulation comprising: a) a fraction of fine particles made of a mixture composed of 90 to 99.5 percent by weight of particles of alpha-lactose monohydrate and 0.5 to 10 percent by weight of particles of magnesium stearate, said mixture having a mass median diameter lower than 20 micron; b) a fraction of coarse particles constituted of alpha-lactose monohydrate having a mass median diameter equal to or higher than 100 micron, wherein the ratio between the fine particles and the coarse particles is between 1:99 and 30:70 percent by weight; and c) formoterol fumarate dihydrate in combination with beclometasone dipropionate as active ingredients both in form of micronized particles; said process comprising the steps of: i) co-micronizing the alpha-lactose monohydrate particles and magnesium stearate particles of fraction a); and ii) mixing the fraction of co-micronized particles a), and the fraction of coarse particles b) with both active ingredients in micronized form; wherein i) no more than 10% of said BDP particles have a volume diameter lower than 0.6 micron and the d(v,0.1) is comprised between 0.8 and 1.0 micron; ii) no more than 50% of said particles have a volume diameter comprised between 1.5 micron and 2.0 micron and the d(v,0.5) is comprised between 1.5 and 2.0 micron; and iii) at least 90% of said particles have a volume diameter lower than 4.7 micron and the d(v,0.9) is comprised between 3.0 and 4.0 micron; and wherein the BDP particles have a particle size span, defined as ⌈ d v 0.9 − d v 0.1 ⌉ / d v 0.5, comprised between 1.2 and 2.2; and whereby said volume diameter is determined by laser diffraction using a Malvern apparatus. a) a fraction of fine particles made of a mixture composed of 90 to 99.5 percent by weight of particles of alpha-lactose monohydrate and 0.5 to 10 percent by weight of particles of magnesium stearate, said mixture having a mass median diameter lower than 20 micron; b) a fraction of coarse particles constituted of alpha-lactose monohydrate having a mass median diameter equal to or higher than 100 micron, wherein the ratio between the fine particles and the coarse particles is between 1:99 and 30:70 percent by weight; and c) formoterol fumarate dihydrate in combination with beclometasone dipropionate as active ingredients both in form of micronized particles; said process comprising the steps of: i) co-micronizing the alpha-lactose monohydrate particles and magnesium stearate particles of fraction a); and ii) mixing the fraction of co-micronized particles a), and the fraction of coarse particles b) with both active ingredients in micronized form; wherein i) no more than 10% of said BDP particles have a volume diameter lower than 0.6 micron and the d(v,0.1) is comprised between 0.8 and 1.0 micron; ii) no more than 50% of said particles have a volume diameter comprised between 1.5 micron and 2.0 micron and the d(v,0.5) is comprised between 1.5 and 2.0 micron; and iii) at least 90% of said particles have a volume diameter lower than 4.7 micron and the d(v,0.9) is comprised between 3.0 and 4.0 micron; and wherein the BDP particles have a particle size span, defined as ⌈ d v 0.9 − d v 0.1 ⌉ / d v 0.5, comprised between 1.2 and 2.2; and i) co-micronizing the alpha-lactose monohydrate particles and magnesium stearate particles of fraction a); and ii) mixing the fraction of co-micronized particles a), and the fraction of coarse particles b) with both active ingredients in micronized form; wherein i) no more than 10% of said BDP particles have a volume diameter lower than 0.6 micron and the d(v,0.1) is comprised between 0.8 and 1.0 micron; ii) no more than 50% of said particles have a volume diameter comprised between 1.5 micron and 2.0 micron and the d(v,0.5) is comprised between 1.5 and 2.0 micron; and iii) at least 90% of said particles have a volume diameter lower than 4.7 micron and the d(v,0.9) is comprised between 3.0 and 4.0 micron; and wherein the BDP particles have a particle size span, defined as ⌈ d v 0.9 − d v 0.1 ⌉ / d v 0.5, comprised between 1.2 and 2.2; and