The present invention involves an improved process for the preparation of Indocyanine green of Formula (I) having high purity of about 99% wherein the process comprises steps of reacting 112-trimethyl-1H-benzo e indole with 14-butane sulfone in boiling solvent to give 4-(112-trimethyl-1H-benzo e indolium-3-yl)butane-1-sulfonate. Followed by reacting 4-(112-trimethyl-1H-benzo e indolium- 3-yl)butane-1-sulfonate of Formula (IV) and N-phenyl-N-((1E3E5E)-5-(phenylimino)penta-13-dienyl)acetamide of formula (V) in presence of sodium acetate and alcohol and extracting the title compound formula (I) with an ester solvent.
