A conformational study on the preferred minima D (C7ax) of N-For-L-Cys-NH2 in isolated state was carried out using multi niche crowding genetic algorithm coupled with semi empirical-method AM1 (AM1/GA-MNC). All conformations located were subjected to geometry optimization at the HF/3-21G and the HF/6-31G++ (d, p) levels of theory. Six of the nine side-chain conformers were located and are É£D[g-, g+], É£D [g-, g-], É£D[g-, a], É£D[a, g-], É£D[a, g+] and É£D[g+, g-], no conformational migrations were observed. All these structures are stabilized by the hydrogen bond associated with the seven-member ring of the É£ backbone conformation C=O…H-N. Two conformers had side chain-backbone intramolecular hydrogen bonding S-H…O=C at AM1/GA-MNC and HF/3-21G.