Thymus, an aromatic medicinal plant, is a well-known, perennial and woody herb from Lamiaceae family. The use of the extracts and herb of thyme plants as antibacterial, antioxidant, natural food preservative and in cosmetic industry has increased the economic importance of this medicinal crop worldwide [1]. Thymus is taxonomically a very complex genus with a high frequency of hybridization and introgression among sympatric pecies, and some species of this herb are endemic to Iran[2]. This study was carried out in order to evaluate yield and yield components in fourspecies ofT.daenensis, T. migricus, T. kotschyanus and T. pubescens collected from Semnan, west Azerbaijan, Qazvin and East Azerbaijan respectively. This experiment was performed in a randomized completeblocks design with three replications at the Research Station of the Faculty of Agriculture, Ferdowsi University of Mashhad. Inflorescence length, number of flowers per inflorescence, shoot height, leaf length, leaf width, the largest and smallest diameter of canopy, 1000-grain weight, fresh and dry herb yield, were measured.Analysis of variance the data showed that there was considerable variation for all studied characters. Results of mean comparisons showed that the highest dry and fresh herb yield per plant were 117.8 and 400.6 gr for T.daenensis, respectively. The lowest yield was recorded for T. migricus. Maximum inflorescencelength, number of flowers per inflorescence, the largest diameter of canopy and leaf length was also recorded for T. daenensis. A positive significant correlation was observed between dry yield per plant and the largest diameter of canopy, leaf length, and fresh yield. Correlation between dry herb yield per plant and leaf width was strongly negative. T. daenensis produced more essential oil as compared to another thyme species. Salami and Rahimmalek reported that the fresh and dry shoot yield of T. daenensis were 7197 and 1321(kg per ha) in first years, 10310 and 1176 (kg per ha) in second year

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