Recently, mobile networks and radio frequency identification (RFID) technologies are both widely applied by many enterprises to develop their applications. The third-generation (3G) mobile network technology is one of the popular mobile network technologies because service providers can serve users anytime and anywhere through 3G mobile network technology. A solution that combines RFID technology with 3G mobile network technology could identify users anytime and anywhere. However, RFID tags are limited in computation power and suffered from security threats, especially on mobile networks. An authentication with low-cost RFID tags in Mobile Networks should be proposed in this paper. This paper designs a key agreement mechanism to achieve consistency, integration, legality, and safety. In order to design a low-cost scheme, our authentication mechanism is built of simple XOR operations and one-way hash function. Although the computation cost of our proposed mechanism is not the best, our proposed mechanism can achieve more security requirements for practical applications. Copyright © 2013 John Wiley & Sons, Ltd.