The invention relates to a improved process for the preparation of Losartan and its potassium salt, which comprises: (i) reacting bromo OTBN with BCFI in the presence of a base and a phase transfer catalyst to produce a cyano aldehyde; reacting the formed cyano aldehyde with sodium azide in the presence of tributyl tin chloride to produce aldehyde tetrazole; reducing the formed aldehyde tetrazole with sodium borohydride to produce Losartan; and, if desired, converting the formed Losartan to its potassium salt by known method.