Abstract: Described herein is a fixed dose pharmaceutical composition containing arformoterol or its salt and a glycopyrronium salt. Particularly, a fixed dose pharmaceutical composition in the form of an aerosol or an aerosolizable for inhalation administration includes arformoterol or its salt, a glycopyrronium salt, and pharmaceutically acceptable excipients. Also described is a process for preparing the compositions and their use for the treatment of asthma and/or chronic obstructive pulmonary disease in a subject in need thereof. Also described are pharmaceutical compositions that include an effective amount of arformoterol (or its salt), a glycopyrronium salt or their combination in the form of a suspension or solution, and methods of their preparation.