The yield and composition variation of the essential oil from Thymus capitatus Hoffmanns. et Link., an aromatic plant which grows in the wild state in the area of Korba (Tunisian Cap Bon) were determined. Essential oil was obtained by steam distillation apparatus at atmospheric pressure. The yield in essential oil showed a maximum at the flowering stage (1.08-2%) and a minimum during the dormancy period (about 0.2%). Analysis was performed by GC and GC-MS. The composition also showed different patterns at different phases of the vegetative cycle. At the flowering period the essential oil is rich in carvacrol. p-Cymene showed a variation with a maximum at the minimum of carvacrol.