An efficient microwave-assisted extraction (MAE) technique has been developed to extract thymol from seeds of Trachyspermum ammi. The maximum percentage extraction of thymol reached 99% in 45 min under the optimal MAE conditions at 45 degrees C of extraction temperature and 1:30 (g of material/cm(3) of solvent). The MAE showed obvious advantages in terms of short duration and high efficiency to extract thymol in comparison with conventional solvent extraction techniques. Scanning Electron Microscopy photographs of un-irradiated and irradiated seeds corroborate the enhancement observed in the rate and percentage extraction of thymol from T. ammi seeds. Experimental data at different conditions were fitted with a steady state model proposed by Wongkittipong et al. (2004) [21]. The effective diffusion coefficient for thymol varies from 0.6539 x 10(-13) to 1.300 x 10(-13) m(2)/s for microwave irradiated dry seeds. In case of microwave irradiated solvent-soaked seeds, effective diffusivity varies from 1.435 x 10(-13) to 2.39 x 10(-13) m(2)/s at different solvent-soaking times. Whereas for extraction in microwave reactor under controlled conditions effective diffusivity varies from 1.835 x 10(-13) to 3.241 x 10(-13) m(2)/s. The order of magnitude of effective diffusivity estimated in the present work agrees well with that of andrographolide from Andrographis paniculata. (C) 2009 Published by Elsevier B.V.