Abstract: A three-time-slot two-way relaying protocol, named as two-way selective decode-and-forward (TW-SDF) protocol, was proposed. This relaying protocol integrates network coding and the selective decode-and-forward method, and was tailored for wireless networks with simple devices, like sensor networks. Compared with the well-known physical-layer network coding protocol, the considered TW-SDF has the merits of full diversity order gain, low encoding and decoding complexity and easy-to-implement. Provided block codes, an upper bound on the block error rate of TW-SDF was derived and proved, which is valid for all hard decoders. Simulation results further verify that the upper bound is remarkably tight if BCH codes are utilized.