Iran is among the top 10 countries in the world in tomato production. Damping off is one of the most destructive tomato diseases, caused by Fusarrium oxysporum. This fungus spreads through the soil and tissues infested by the plant on the farm's surface. The disease has a wintering and shelf life in the soil and plant remains, which, by providing the appropriate temperature and humidity conditions, are introduced into the plant tissue through rooting. The disease factor in wet soils and temperatures of 28 ° C, as well as the shortage of nitrogen, phosphorus and calcium elements, have better conditions for expansion. Today, biological control of plant diseases is becoming an alternative for chemical pesticides due to increased levels of safety and health and the least environmental impact. In this research, biological control of tomato wilt disease was investigated using two Trichoderma strains, one commercial (Trichoderma harzianum T-22) and one native to Iran (T. harzianum AS12-2), in in vitro conditions. The dual culture test results showed that both strains considered as Class 2 of antagonism according to the the system of Bell et al. (1982) where they had overgrowth and conidiation on the pathogen colony. The volatile metabolites of strains T-22 and AS12-2 inhibited the growth rate of F. oxysporum by 29% and 23.5%, respectively. The microscopic examination on slide, showed that both Trichoderma strains grew toward F. oxysporum hyphae and coiling fragmented mycelia were observed. Overall, the results indicated that the native Trichoderma strain also have the potential to commercialize. Greenhouse tests are in progress.