ABSTRACT
This reasearch was conducted to study the phenotypic diversity of Thymus kotschyanus populations. Seeds were collected from natural inhabitats (Guilan, Mazandaran, West Azarbaijan, Semnan and Qazvin) and planted in Qom reasearch station in 2007. A number of some such different morphological and phenological traits of the plants as plant^,s height, leaf length, leaf width, oil content, internode length, diameter of inflorescence and flowering stage as well as full bloom were evaluated. Analysis of Variance revealed significant differences among  populations in all the studied traits except for the cases of peduncle length and diameter of inflorescence. Results of simple correlation analysis revealed the existence of significant correlations among some of the plant^,s important characterstics. One of the most conspicuous traits of the plant, namely oil content was in significant positive correlation with the number of flowers per inflorescence and with internode length while being in negative correlation with fresh weight, leaf length as well as leaf width. Factor analysis was also carried out for defining of the determinant factors and the traits constituting each factor. A number of  5 main and indipendent factors explained over 82.9% of the total variation related to the main effective characterstics. Populations of  the plant were separated into six groups as by cluster analysis and through Ward method. Populations of Mazandaran 2 contained the most oil content (2.5%) as well as the  number of flowers per inflorescence, two highly desirable traits to be employed in the plant^,s breeding programs.