Recently, the mobile communication became indispensable to the life of modern people. The technology of radio communication is developed and complicated gradually. But, existing radio system is possible to use only one service, so new communication technology is required. The new technology is that one communication system is possible to provide the multiplex service. This new system must satisfy various service frequency bandwidths. The power amplifier is a core device in the radio communication system. Small-size and efficiency improvement are important factors of modern communication system. To improve efficiency and small-size, this paper proposed a dual-band power amplifier using a transistor. This proposed power amplifier is fabricated and measured. The output powers are 31.2 dBm and 31.5 dBm and the power gains are 9.2 dB and 9.5 dB, at 1.8 ㎓ and 2.2 ㎓, respectively. The measured output power and gain show better results than the simulation at 1.8 ㎓, also they show not so bad results at 2.2 ㎓. If the characteristics at 2.2 ㎓ are improved, this proposed amplifier will be used as HPA for IMT.