The inhibitory effects of plant essential oils on seed germination and on seedling growth of weeds were investigated in petri dish experiments. Essential oils were extracted from leaves and flowers of five different plant species (Artemisia vulgaris L., Mentha spicata L. subsp. spicata, Ocimum basilicum L., Salvia officinalis L., Thymbra spicata L. subsp. spicata) collected from Tokat region of Turkey. Bioherbicidal activities of essential oils were assayed in four concentrations (2, 5, 10 and 20 mu l) against eight weed species from different families (Agrostemma githago L., Amaranthus retroflexus L., Cardaria draba (L.) Desv., Chenopodium album L., Echinochloa crus-galli (L.) P.B., Reseda lutea L., Rumex crispus L., Trifolium pratense L.).