Mobile adhoc network is a special kind of wireless networks. It is a collection of mobile nodes without having aid of establish infrastructure. In mobile adhoc network, it is much more vulnerable to attacks than a wired network due to its limited physical security, Securing temporal networks like Mobile Ad-hoc Networks (MANETs) has been given a great amount of attention recently, though the process of creating a perfectly secured scheme has not been accomplished yet. MANETs has some other features and characteristics those are together make it a difficult environment to be secured. The bandwidth of MANET is another challenge because it is unlikely to consume the bandwidth in security mechanisms rather than data traffic. This paper proposes a security scheme based on Public Key infrastructure (PKI) for distributing session keys between nodes. The length of those keys is decided using intuitionistic fuzzy logic manipulation. The proposed algorithm of Security-model is an adaptive intuitionistic fuzzy logic based algorithm that can adapt itself according to the dynamic conditions of mobile hosts. Finally the Experimental results shows that the using of intuitionistic fuzzy based security can enhance the security of (MANETs).