Thymus persicus (Lamiaceae) is a range-restricted endemic medicinal and aromatic plant from northwest of Iran. Due to the medicinal importance and over-exploitation of the plant from its natural habitats, conservationand ex situ cultivation of the plant is needed. In the present study, essential oil variability of the plant during its in vitro conservation including in vitro regenerated plant (RP) and acclimated plant (AP) was assessed by GC-FID and GC-MS, and compared with those of growing wild plant (WP). In total, 44, 25 and 25 compounds representing 98.5%, 98.7% and 98.1% were identified in the oils of WP, RP and AP, respectively. The major identified components in the oils were 4,8-Î²-epoxy-caryophyllene (2.3â10.7%), Î±-terpineol (9.5â39.2%), linalool (5.7â15.7%) and thymol (2.6â32.8%). In vitro RP with the highest content of thymol had the greatest distance with WP. The AP was also significantly dominated with a large difference in Î±-terpineol.