Considering security as well as cost-efficiency, various unified and scalable hardware architectures for Public Key Cryptosystems such as RSA and ECC have caused wide concern.In most cases, the efficient implementation of modular multiplication is the corner stone of the system overall performance.In our work, Residue Number System (RNS) has been employed to implement Montgomery Multiplication.In this way, a large integercan be decomposed into several small and dependent elements.As a result, RNS owns the attractive ability to execute modular arithmeticin parallel.In this talk, two kinds of hardware architec tures we proposed for Montgomery Multiplication in RNS are introduced, one for prime field(Fp)and one for binary extension field(F2m),respectively.The experiment results show that the proposed architectures can achieve better tradeoff among algorithm flexibili ty, performance and area than other related works.