Effect of the antifungal antibiotic gliotoxin on root-rot diseases caused by Fusarium solani and its influence on population of fungal flora in soil were investigated. Bean seeds were treated with different concentrations of gliotoxin before sowing. The results obtained from the green house application of bioagent indicated that soaking seeds in different concentrations of gliotoxin from 1μg/mL to 15μg/mL (for 60 minutes) significantly reduced the percentage of damping off and root rot as compared with control (pathogen only). Also 10μg/mL of gliotoxin was significantly decreased the population of fungal flora as compared with control.