Here, the seeds of 10 different species of the Yarrow (Achillea spp.) originated from geographically different regions of Iran were planted in the greenhouse of medicinal garden of Hamedan (2017-2018), and subsequently phytochemical variation of the essential oils of each individual species collected before and after flowering were assessed using GS-MS. Before flowering, overall, 27 metabolites were detected, among which 1,8-cineol, artemesia alcohol, artemesia ketone, camphor, germacrene-D, linalool, Terpineol and nerolidol were the superior. The maximum amounts of 1,8-cineol was observed in A. alepica, A. eriophora, A. biberstinii, A. filipendula, and A. nobilis, while both A. alepica and A. eriophora contained the highest amounts of camphor. Meanwhile, here, the maximum amounts of Germacrene D were acquired in A. tenuifolia (43.19%) and A. wilhelmsii (47.03%). Upon flowering, overall, 78 metabolites were detected, among which Cubenol, Eucalyptol, Camphor, germacrene-D, sabinol, trans-Nerolidol, Chamazulene, Chamazulene, and 2-Cyclohexen-1-ol, 1-methyl-4-(1-methylethyl)-, cis- were the superior. Based on cluster analysis and PCA constructed by the metabolite data of before and after flowering, all the 10 species of the genus Achillea were respectively grouped into three and four distinguished categories. Lastly, the results indicated that both quantity and quality of chemical composition of yarrow essential oils could be influenced by species under study, various growth and development stages, genetic background and possibly geographical/climatological factors, and that there is an acceptable phytochemical variation among them.