Abstract: Soil microorganisms have been shown to possess several mechanisms capable of altering metal bioavailability for uptake into roots. In addition, root mycorrhizal associations have been shown to affect the rate of metal uptake. There is evidence that exposure of plants to excess concentrations of heavy metals such as Cu results in oxidative injury. In this study, effect of arbuscular mycorrhizal fungus Glomus etunicatum on tolerance of Cu toxicity in tomato plants was studied. In order to prepare seedling medium, we used washed and sterilized sand and agricultural soil. Tomato seeds were surface sterilized and planted in two pots. One filled just with sterilized sand (for non-mycorrhizal treatments) and the other filled with sterilized sand mixed with G. intraradices mycorrhizal inoculum. We were certain about complete colonization after 4 weeks, so we transferred three seedlings to each main pot. Plants grew in growth chamber for nine weeks. During growth period plants received modified Hoagland’ s solution (with half P content) with Cu concentration of 0, 1.5, 3.5, 5.5, 7.5 mM CuSO4 in triplicates. Antioxidant enzymes activity, Ascorbate Peroxidase (APX) and Guaiacol Peroxidase (GPX) and Root Length Colonization (RLC) percentage in mycorrhizal and non-mycorrhizal plants were measured. APX activity in mycorrhizal shoots increased but there was no significant correspondent increase in roots of these plants. GPX activity in mycorrhizal roots increased but there was no significant correspondent increase in shoots of these plants. Activity of this enzyme in roots and shoots of mycorrhizal plantshigher than non-mycorrhizal plants. Estimation of root length colonizatinon by gridline intersect method, increase in Cu concentration, colonization percentage decreased significantly. The data show the possible role of mycorrhiza in plant protection against Cu toxicity.