The present invention relates to the process of differentiation of natural (−)-menthol from synthetic menthol using the GC-MS technique. First, menthol is solubilized in organic solvents such as hexane, dichloromethane, methanol, ethanol, etc. Then, the solution is injected through GC-MS and analytical parameters are set in such a manner that the major compound menthol is not detected under the operating conditions. As a result, peaks of interest get enhanced; the baseline is separated and detected in a single quadrupole mass spectrometer. The natural (−)-menthol contained p-menthenol as its unique identifier, along with other common impurity peaks such as p-menthenone and p-menthanol isomers. On the contrary, synthetic menthol did not contain p-menthenol as a distinguishing marker. The process is very easy, economical and quickly differentiates the natural menthol through GC-MS modified technique.