This letter presents a novel dual‐band balun using the branch‐line configuration. We establish design equations for dual‐band balun based on the even‐odd mode method. The proposed circuit operates at 2.45 GHz and 5.25 GHz. The single‐ended power is divided differentially at the balanced ports. The insertion losses (S21 and S31) show around −2.7 dB to −4.3 dB at the two different frequencies. The phase difference between the balanced ports shows maximum 3° deviation from 180°. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 52: 642–644, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24996