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A B S T R A C T Mobile Ad hoc network (MANET) is an example of mobile wireless network characterized by dynamic topology, self-organization, auto-configuration, lack of infrastructure and decentralize administrator that made it more useful in military battlefield, smart building and emergency rescue. The nodes vulnerability in MANET security becomes the center of creative research efforts. Many security schemes were proposed, rather than trying to encompass the entire field of MANET security. In this paper the same security issue was addressed by evaluating the performance of two reactive protocols Ad-hoc On-demand Distance Vector (AODV) protocol and Reverse Ad-hoc On-demand Distance Vector under jellyfish attacks. This research adopts the use of Network simulator 2.35 to test the two reactive protocols vulnerability in the presence of jellyfish attacks. The results of the performance metrics shown that the two protocols average throughputs were affected in the presence of the attacks and increase tremendously as the number of node increases, while packet delivery ratio decrease with increase in number of malicious nodes. The jellyfish attacks have great effect in number of packet drop in the protocols. Less packet drop in the presence of single jellyfish but greatly increase as more threats were introduced and maintain the increase rate as the number of attacks increase. The experimental results for all scenarios shown that the higher the jellyfish attacks on AODV and RAODV the lower the performance of the two protocols.