This paper presents a novel technique for decoupling of two closely spaced dual-band antennas using T-stub circuits. A decoupling circuit consists of three T-stub elements, each of which provides the required phases and impedances in dual frequency bands independently. A set of general design formulas is derived for determining the electric parameters of required T-stubs. To validate the new decoupling technique, a pair of dual-band inverted-F antennas working in the 2.45- and 5.8-GHz bands and another pair of dual-band monopole antennas working in the 2.4- and 5.2-GHz bands with and without the decoupling circuit are designed, prototyped, and measured. The measured S-parameters correlate with the theoretical designed data very well. With the decoupling circuit, significant improvement in antenna efficiency and data throughput demonstrates that the technique is useful for wireless terminals, where dual-band multiple-input and multiple-output antennas are used.