The invention provides a method for the preparation of fentanyl comprising: (a) reacting 4-piperidone hydrochloride monohydrate with aniline in presence of reducing environment to produce 4-anilinopiperidine (4-AP), (b) reacting the 4-AP as obtained from step (a) with phenethyl halide under reflux conditions in highly alkaline medium to give 4-anilino-N-phenethylpiperidine, and (c) converting the 4-anilino-N-phenethylpiperidine to fentanyl by reacting with propionyl chloride in presence of halogenated hydrocarbons, then isolating fentanyl by solvent extraction and purifying by crystallization from petroleum ether at a temperature ranging from 60-80° C.