Flutamide (2-methyl-N-[4-nitro-3-(trifluoromethyl)phenyl]-propanamide) is a non-steroidal drug that has a specific anti-androgenic activity so that it is used in the treatment of prostate cancer. A simple method for extraction and detection of flutamide from pharmaceutical forms are reported using Soxhlet apparatus combined electrospray ionization tandem mass spectrometry (ESI(−)-MSn, n = 1−4) in negative ion mode. Spectra show a fingerprint peaks corresponding to flutamide. Propanamide moiety plays important role in structure elucidation. The diagnostic ions produced a useful fingerprint maps to identify flutamide in unknown samples. Furthermore, the proposed ions may help in the metabolite studies of the drug. The method proposed here is easy, cheap and applicable for large quantity.