The present invention relates to an amorphous form of vilanterol trifenatate, processes for its prepn. and its use in pharmaceutical formulations for the treatment of respiratory diseases, particularly for the treatment of asthma and chronic obstructive pulmonary disease.  In particular, the invention relates to an amorphous form of vilanterol trifenatate, characterized by the x-ray powder diffraction (XRPD) pattern, obtained using copper K-α1 radiation.