Canola black leg caused by Phoma lingam, is one of the most important and prevalent disease of canola through the world and as well as North Iran. Nowadays using antagonistic agent for controlling of plant diseases is recommended instead of using chemicals. Trichoderma isolates can control pathogens via different mechanisms. In this research, the effect of Trichoderma harzianum and T. atroviridae against P. lingam was investigated in the laboratory and greenhouse. Laboratory tests were done as dual culture and testing of the fungal volatile compounds. In the greenhouse, the antagonistic effects of theisolates were tested through treating rapeseed seeds and rapeseed above-ground parts with the spore suspension of the isolates in 106 spore per ml. The experiments were done in complete randomized design with four replications. Percent of plant mortality and disease severity were assessed. All isolates showed antagonistic activities against fungal phytopathogen. The two isolates T. harzianum and T. atroviridae could inhibit the growth of the pathogen by 79.2 and 80.2 respectively in dual culture. In volatile compound phase, percent of growth inhibition were 15-21% and 31-39% in 120 and 240 hours after culture. In greenhouse tests, antagonistic species could significantly (P<0.01) reduce disease severity compared to control. The greenhouse results revealed that in the seed treatment experiment, Trichoderma isolates decreased the rapeseed blackleg to 42.5 and 47.5℅, respectively after two weeks. Treating the above-ground parts with isolates T. harzianum and T. atroviridae decreased the disease to 63.13 and 78.79℅, respectively. So both Trichoderma species can biologically inhibit canola black leg, but T. atroviridae was more effective than another one. Considering the harmful effects of chemical fungicides, using these microbial agents is essential.