NOVELTY - Preparation of aprepitant (A1) involves a) condensing 2-(R)-((1R)-1-(3,5-bis(trifluoromethyl)phenyl)ethoxy)-3-(S)-(4-fluorophenyl)morpholine hydrochloride salt with 2-(2-chloro-1-iminoethyl)hydrazinecarboxylic acid methyl ester to obtain reaction mixture containing 2-(2-((2R,3S)-2-((1R)-1-(3,5-bis (trifluoromethyl)phenyl) ethoxy)-3-(4-fluorophenyl)-4-morpholinyl)-1-iminoethyl)hydrazinecarboxylic acid methyl ester (A2); b) in-situ cyclizing (A2) to (A1) by heating reaction mixture at low temperature, where steps (a) and (b) are carried out without isolating intermediates from mixture.    USE - For preparation of 5-(((2R,3S)-2-((1R)-1-(3,5-bis (trifluoromethyl)phenyl) ethoxy)-3-(4-fluorophenyl)-4-morpholinyl) methyl)-1,2-dihydro-3H-1,2,4-triazol-3-one (aprepitant) (claimed) for treatment of acute and delayed chemotherapy induced nausea and vomiting, and for prevention of postoperative nausea and vomiting.    ADVANTAGE - The aprepitant can be obtained in good yield and purity (i.e. yield of greater than or equal to 75% and purity of greater than or equal to 99.5%) from 2-(R)-((1R)-1-(3,5-bis(trifluoromethyl)phenyl)ethoxy)-3-(S)-(4-fluorophenyl)morpholine hydrochloride salt (II) through an improved process, which involves in-situ preparation of aprepitant, avoids isolation of 2-(2-((2R,3S)-2-((1R)-1-(3,5-bis (trifluoromethyl)phenyl) ethoxy)-3-(4-fluorophenyl)-4-morpholinyl)-1-iminoethyl)hydrazinecarboxylic acid methyl ester using any work-up processes such as extraction, evaporation, crystallization. Also, the process avoids the use of large volume of organic solvent for condensation of compound (II) with 2-(2-chloro-1-iminoethyl)hydrazine carboxylic acid methyl ester (III) and high temperature required for the cyclization of 2-(2-((2R,3S)-2-((1R)-1-(3,5-bis (trifluoromethyl)phenyl) ethoxy)-3-(4-fluorophenyl)-4-morpholinyl)-1-iminoethyl)hydrazinecarboxylic acid methyl ester (IV) to obtain aprepitant. Thus, the process provides a simple, cost- effective and industrially applicable process for the preparation of aprepitant. The process avoids use of any work-up processes involving extraction, evaporation, crystallization, to isolate the compound (IV) in the form of solid, foam, viscous liquid or liquid.    DETAILED DESCRIPTION - Preparation of 5-(((2R,3S)-2-((1R)-1-(3,5-bis (trifluoromethyl)phenyl) ethoxy)-3-(4-fluorophenyl)-4-morpholinyl) methyl)-1,2-dihydro-3H-1,2,4-triazol-3-one (aprepitant) (A1) (I) involves a) condensing 2-(R)-((1R)-1-(3,5-bis(trifluoromethyl)phenyl)ethoxy)-3-(S)-(4-fluorophenyl)morpholine hydrochloride salt (II) with 2-(2-chloro-1-iminoethyl)hydrazinecarboxylic acid methyl ester (III) in the presence of potassium carbonate and dimethylsulfoxide to obtain a reaction mixture containing 2-(2-((2R,3S)-2-((1R)-1-(3,5-bis (trifluoromethyl)phenyl) ethoxy)-3-(4-fluorophenyl)-4-morpholinyl)-1-iminoethyl)hydrazinecarboxylic acid methyl ester (A2) (IV); b) in-situ cyclizing the reaction mixture containing compound (A2) (IV) to the compound (I) by heating reaction mixture in a mixture of dimethylsulfoxide and a polar protic solvent at a low temperature; and c) isolating aprepitant (I), where the steps (a) and (b) are carried out without isolating intermediates from the reaction mixture.