The present invention relates to improved processes for the preparation of endolthelin receptor antagonists darusentan and ambrisentan, their salts and intermediates. Processes for the preparation of darusentan and ambrisentan comprise reacting benzophenone with a compound of Formula-3 to provide a compound of Formula-4, which on in-situ treatment with methanol and a suitable acid provides a compound of Formula-5; hydrolyzing the compound of Formula-5 to provide a compound of Formula-6; resolving the compound of Formula-6 to provide a compound of Formula-7; esterifying the compound of Formula-7 to provide a compound of Formula-8; reacting the compound of Formula-8 with a compound of Formula-9 to provide a compound of Formula-10; hydrolyzing the compound of Formula-10 to provide darusentan or ambrisentan; and purifiying darusentan or ambrisentan to provide darusentan or ambrisentan having purity greater than 99.00% by HPLC.