The present invention provides an improved process for preparation of 1-[2-(2,4-dimethyl-phenylsulfanyl)-phenyl]-piperazine; commonly known as vortioxetine (referred to as the compound (I)) and pharmaceutically acceptable salts thereof; wherein the process comprises reaction of 2-((2,4-dimethylphenyl)thio)aniline (II) with bis(2-alkyl)amine (IIIa) or its salt in the presence of a cyclic amide solvent.