Disclosed is a process for the preparation of montelukast sodium. The process comprises a) reacting 2-(2-(3(S)-(3-(2-(7-chloro-2-quinolinyl)-ethenyl)phenyl)-3-hydroxypropyl)phenyl)-2-propanol with methane sulfonyl chloride and coupling the resultant mesylate compound with 1-(mercaptomethyl)cyclopropane acetic acid in presence of a base and free alkali source followed by saltification with an amine in a single step reaction and b) converting the montelukast amine salt to montelukast sodium salt.
