The essential oils and hexane extracts of four Achillea species were analyzed by GC/MS. Achillea biserrata Bieb., Achillea wilhelmsii C. Koch and Achillea biebersteinii Afan oils contained mainly 1,8-cineole (38.1-14.4%), camphor (46.6-23.6%) and borneol (11.7-2.9%,). Achillea coarctata Poir. oil had more different composition, with its main components being viridiflorol (37.7%), alpha-cadinol (8.9%) and cubenol (6.1%). The hexane extracts of A. wilhelmsii, A. coarctata and A. biebersteinii had high percentages of camphor (44.7%, 16.2% and 18.0%, respectively) and 1,8-cineole (19.5%, 30.8% and 165.1%, respectively), whereas the most abundant components in A. biserrata extract were ethyl oleate (13.1%), n-nonadecane (11.3%), and n-eicosane (11.3%). Herbicidal activities of the oils and hexane, acetone and methanol extracts of four Achillea species were assessed against six weed species and germinations, root and shoot growths of weed species were significantly inhibited by both the oils and extracts. In the pest toxicity assay on Leptinotarsa decemlineata, the oils showed toxic effect against the pest. According to the present results, Achillea species could be used as alternative bio-insecticides and bio-herbicides.