This study was conducted to assess the allelopathic effect of essential oils (EOs) obtained from the aerial parts of two different ecotypes (ECTPs A and B) of Zataria multiflora Boiss. with the aim of evaluating their in vitro germination and growth inhibition potential. Gas chromatography (GC) and GC-mass spectrometry (GC-MS) analysis of the oils revealed that carvacrol and linalool (77.4% and 90.6%) were the two major oil components in ECTPs A and B, respectively, which were regarded as two different chemotypes. Other important volatile compounds found in ECTP A were α-pinene (2.7%), p-cymene (7.9%) and γ-terpinene (3.5%). However, in ECTP B these compounds were in lesser amounts and γ-terpinene was not detected. The inhibitory effects of both EOs of ECTPs at concentrations of 0, 80, 160, 320 and 640 µL L⁻¹ on the seed germination and seedling growth of four noxious weeds were evaluated. A significant reduction (p ≤ 0.05) in germination rate, seedling length, root and stem fresh and dry weights were observed by ECTPs; the highest suppressing effect was observed at 320 and 640 µL L⁻¹. The results reported in this study suggest that herbicidal properties of the two ECTP oils could be attributed to their major components.