Crystalline form V of agomelatine (I) is new. Crystalline form V of agomelatine ((I)； N-[2-(7-methoxy-1-naphthyl)ethyl]acetamide) having powder X-ray diffraction diagram, measured using a diffractometer (copper anticathode) and expressed in terms of inter-planar distance d (8.979-3.239 A[deg]), Bragg's angle 2 theta (9.84-27.51 degrees), intensity and relative intensity (15-100 percentage with respect to the most intense), is new. Independent claims are included for: (1) the preparation of (I)； and (2) a composition comprising (I) and, inert and non-toxic carriers. ACTIVITY : Hypnotic； Tranquilizer； Antidepressant； Cardiovascular-Gen.； Sedative； Muscular-Gen.； Immunomodulator； Neuroleptic； Anorectic； Anticonvulsant； Antidiabetic； Antiparkinsonian； Nootropic； Antimigraine； Neuroprotective； Endocrine-Gen.； Contraceptive； Cytostatic. MECHANISM OF ACTION : Melatoninergic receptor agonist.
