Abstract The leaves of Thymus fallax Fisch. et C.A. Mey. were collected from Hamedan (the center of Hamedan province) in the west of Iran and hydrodistilled to produce a light-yellow oil at the yield of 2.5% (based on dry leaves). The oil was analyzed by GC and GC/MS. Twenty-three compounds were identified, among which thymol (65.9%) and Î³-terpinene (10.8%) were the major constituents.