Since a Mobile Ad hoc NETwork(MANET) is a distributed and self-organized network, there could be malicious nodes that intentionally falsify or drop packets. Recently, a number of trust-based secure routing protocols have been proposed for evading those malicious nodes in communication paths. However, two problems still remain. One problem is that trust itself might be falsified and a node might spoof its ID. The other is that most of calculated trusts are not used and expired. In this paper, we propose a scheme to evaluate trust level of communication paths in MANETs using Attribute Certificates (ACs). Using ACs can detect if trust has been falsified, and if a node has spoofed its ID. Moreover, our proposed scheme is able to not only increase security level, but also reduce the number of trust which expire without being used. Simulation results show better packet delivery rate in a path selected by proposed scheme, and improvement of usage rate for calculated trust.