COX-free hydrogen production from ammonia decomposition in a membrane reactor (MR) for PEM fuel cells was studied using a commercial chemical process simulator, Aspen HYSYS®. With process simulation models validated by previously reported kinetics and experimental data, the effect of key operating parameters such as H2 permeance, He sweep gas flow, and operating temperature was investigated to compare the performance of an MR and a conventional packed-bed reactor (PBR). Higher ammonia conversions and H2 yields were obtained in an MR than ones in a PBR. It was also found that He sweep gas flow was favorable for XNH3 enhancement in an MR with a critical value (5 kmol h-1), above which no further effect was observed. A higher H2 permeance led to an increased H2 yield and H2 yield enhancement in an MR with the reverse effect of operating temperature on the enhancement. In addition, lower operating temperature resulted in higher XNH3 enhancement and H2 yield enhancement as well as NG cost savings in a MR compared to a conventional PBR.