With the rapid development of mobile devices, people can easily use various electronic services at any time and anywhere for a convenient and modern life. Remote user authentication becomes a fundamental procedure for network system service to verify whether a remote user is legal through any insecure channel. Users can access many applications, such as Internet banking, online shopping, mobile pay TV, and can run over the Internet or wireless networks. Therefore, secure communications in such wireless environments are increasingly important because they protect transactions between users and servers. Above all, users are vulnerable to attacks and there are many authentication systems proposed to guarantee them. Islam and Biswas proposed a more efficient and secure ID-based system for mobile devices over ECC to improve security for authentication with the key agreement system. They claimed that their system is indeed more secure than previous ones and can resist various attacks. However, it is true because their system is vulnerable to temporary session-specific information attacks and the other system is a denial of service resulting from server database loss. Therefore, the article presents an improvement of their system in order to isolate such problems. Keyword Authentication, Password, Dynamic ID, Smart Card, Impersonation, Session Key, Elliptic Curve Cryptosystem1. Introduction Elliptic curve (EC) systems applied to cryptography were first proposed in 1985 independently by Neal Koblitz and Victor Miller. Elliptic curve cryptography (ECC) is a public key cryptography technique based on elliptic curve theory that can be used to create c...... middle of paper.......[10] “A new remote user authentication system using smart cards,” MS Hwang and LH Li, IEEE Transactions on Consumer Electronics, vol.46, pp. 28-30, February 2000.[11] "A new remote user authentication system for multi-server environments without using smart cards", K.-H. Yeh and N.W. Lo, International Journal of Innovative Computing and Information Control, vol.6, n.8, pp .3467-3478, 2010.[12] “Efficient convertible multi-authenticated encryption system without message redundancy or one-way hash functions,” J.-L. Tsai, T.-S. Wu, H.-Y. Lin and J.‑E. Lee, International Journal of Innovative Computing, Information and Control, 2010.[13] "An authenticated key exchange protocol for mobile stations of two distinct home networks", H.-L. Wang, T.-H. Chen, L.-S. Li, Y.-T. Wu and J. Chen, International Journal of Innovative Computer Information and Control, 2010.