This paper proposes an efficient method for implementing parallel AES-GCM cores using FPGAs. The proposed method improves the performance of the parallel architecture (Throughput/Slice). Presented architectures can be used for applications which require encryption and authentication with slow changing keys like Virtual Private Networks (VPNs). Our architectures were evaluated using Virtex5 FPGAs. It is shown that the performance of the presented parallel AES-GCM architecture outperforms the previously reported ones.