Abstract: This study was conducted with the aim to determine the effect of an hypoaggressive isolate of Fusarium oxysporum on polyphenoloxidase activity in the interaction of date palm with Fusarium oxysporum albedinis, the agent causal of the Bayoud disease. Biochemical analyses indicated that treatment of resistant (BSTN) and susceptible (JHL) date palm seedlings with the hypoaggressive (AHD) or aggressive isolate (ZAG) of Fusarium oxysporum was correlated with the ability of roots to enhance their defense responses. The maximum of polyphenoloxidase activity was revealed to be 5 times higher than in control after 15 and 20 days for ZAG treatment and 3 times after 30 and 40 days for AHD treatment in BSTN and JHL cultivars, respectively. When seedlings were firstly treated by the hypoaggressive isolate and then by the aggressive one, the polyphenoloxidase activity was enhanced within 10 days and reached similar values as obtained by ZAG isolate alone. These results show that polyphenoloxidase induced by the hypoaggressive isolate of Fusarium oxysporum could have an important role in the establishment of date palm resistance against the Bayoud disease.