The essential oils yield of Cedrus atlantica, Chenopodium ambrosioides and Eucalyptus camaldulensis was different. C. ambrosioides gave a relatively higher yield (2.1 ± 0.1%), while that of C. atlantica was low (1.0 ± 0.1%) and that of E. camaldulensis was lower (0.75 ± 0.1% of dry matter). The active ingredients of the essential oils and some of their biological effects were also determined. The characterization of their chemical compositions showed that the three essences have different chemical profiles: C. atlantica was richer in sesquiterpenes (β-Himachalene (54.21%) and γ -Himachalene (15.54%)), C. ambrosioides was very rich in monoterpene peroxides and monoterpenes (α-Terpinene (53.4%), ascaridole (17.7%) and ρ-Cymene (12.1%)) and E. camaldulensis was very rich in monoterpene compounds and monoterpenols (p-cymene (35.11%), γ-Eudesmol (11.9%), L-linalool (11.51%) and piperitone (10.28%)). The in vitro measurement of antioxidant activity by the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) reduction assay showed a significant performance of the eucalyptus oil and average performance of the other two (C. atlantica and C. ambrosioides). The in vitro bio-test for their antimicrobial effects showed that the antibacterial activity differed depending on the essential oil and the concentration used, and that their bactericidal efficacy was similar or superior to that of synthetic antibiotics. The toxicity test on rats revealed that the LD50 of the three essential oils was 500 mg/kg body weight, which classifies them as category four cytotoxic natural products at high doses.