The use of allelopathic compounds is an alternative for weeds control, since they present low toxicity when compared with the synthetic herbicides, that may cause several damages, as the contamination of the environment. Our objective was to determine the chemical composition and allelopathic properties of the essential oils of Psidium cattleianum , P. myrtoides , P. friedrichsthalianum , and P. gaudichaudianum on the germination and root growth of Lactuca sativa and Sorghum bicolor , and to evaluate their action on the cell cycle of root meristematic cells of L. sativa. The main compound found in all the studied species was (E)-caryophyllene ( P. cattleianum —23.4 %; P. myrtoides —19.3%; P. friedrichsthalianum —24.6% and P. gaudichaudianum —17.0%). The different essential oils were tested at different concentrations on L. sativa and S. bicolor , reducing germination, germination speed index, and root and shoot growth of lettuce and sorghum seedlings. The cytotoxicity and aneugenic potential of these oils were evidenced by the reduction of the mitotic index and increase of the frequency of chromosomal alterations in L. sativa . The essential oils of the species of Psidium studied have potential to be used in weeds control.