Wilting or damping off disease is caused by a pathogenic fungi ( Fusarium oxysporum), which considered as as one of the most serious diseases, which lead to a serious threat in the production of one of the most dependent crops in Gaza strip, Capsicum annuum. Two fungi were isolated, Beauveria bassiana which used as biological control agent and F. oxysporum which causes wilt disease. They were cultured and tested in vitro and applied under field conditions. This study approved that the entomopathogenic fungi especially, b. bassiana is safe and significant approach for the biological control of wilt disease caused by F. oxysporum. Evaluation of B. bassiana spores activity, as a biological control agent was carried out using liquid-semi solid fermentation techniques and the entomopathogenic of B. bassiana against growing F. oxysporum was proven. Our results showed a highly significantly effects of B. bassiana against F. oxysporum.