Studying the effect of eight Bacillus isolates on growth of Fusarium oxysporum in vitro and in glasshouse showed that, Bacillus subtilis No.2, Bacillus spp. No.2 and Bacillus subtilis No.1 were the best antagonistic bacteria for limiting growth of F. oxysporum as they caused the highest inhibition zone (35.67, 34,00 and 30.33 mm) respectively. Evaluating the effect of Bacillus culture filtrates at different concentrations on the linear growth and spore germination of Fusarium oxysporum revealed that, all filtrates of the tested Bacillus isolates at 50% concentration completely inhabited spore germination of F. oxysporum. Culture filtrates of Bacillus subtilis No.2 and Bacillus spp. No.2 also were more effective in reducing mycelial growth and reducing the growth of F. oxysporum by 80.74 and 80.37% respectively. On the other hand Bacillus subtilis No.1 and Bacillus spp. No. 4 made lysis to mycelial of F. oxysporum. Generally linear growth and spore germination were decreased by increasing the concentrations of culture filtrate from 10% up to 50%. Effect of treating cucumber seeds with cell suspension of Bacillus isolates on incidence of Fusarium wilt disease in greenhouses, revealed that all isolates were effective in reducing disease incidence and disease severity compared to the control. Bacillus megtla was the best isolate and completely prevented the disease incidence followed by B. subtilis No. 2 and Bacillus spp. No. 2 and reducing the disease severity by 93.33 and 91.67% respectively. Key words: cucumber, fusarium wilt, biological control, Bacillus, greenhouses.