Abstract Essential oils isolated by steam distillation from the aerial parts of Thymus persicus (Ronniger ex Rech. f.) Jalas, before flowering and at the full flowering stage, were analyzed by capillary GC and GC/MS. Among the 25 compounds identified, the major components were carvacrol (39.0% and 27.1%), geraniol (15.7% and 9.4%), p-cymene (7.5% and 10.2%), thymol (6.5% and 11.9%), Î-terpinene (6.1% and 6.5%) and geranyl acetate (5.3% and 5.3%) before flowering and at full flowering stage, respectively.