IN THE present study, the effect of garlic (Allium sativum) and …. onion (Allium cepa) essential oils and water extracts at three concentrations (5, 10 and 15%) on yield and chemical composition of cumin (Cuminum cyminum L.) were investigated. All treatments improved growth parameters (plant height, shoot number and number of umbels /plant) and total seed yield with no effect on the chemical composition of cumin essential oil. Onion water extracts gave the highest total seed yield. Garlic water extracts gave the highest values of total carbohydrate, total protein and total free amino acids. The chemical composition of essential oils extracted from garlic cloves and onion bulbs were fractionated by GC/MS. Major compounds in garlic were allicin and diallyl disulfide followed by dimethyl-trisulfide while in onion were allium thiosulfinate, alkyl thiosulfnates and allyl propyl disulphide.