Here we report the synthesis of ZnO@C coaxial gemel hexagonal microrods with a thin hydrothermal carbon (HTC) layer on their surface by a facile one-step hydrothermal method with furfural as the carbon precursor. The furfural has a unique dual role, which not only induces the nucleation of ZnO in the initial stage of hydrothermal process, but also forms a thin HTC layer deposited on the ZnO surface. The thickness of the surface HTC layer increases with the hydrothermal time until 16 h under the conditions adopted in the present study. It has been found that the HTC layer has resulted in a significant improvement in the photocatalytic activities and photostabilities of the ZnO@C microrods for the UV-irradiated photodegradation of methylene blue solution. The mechanism involved in the process is proposed and discussed in terms of the photodegradation scheme and the properties of the ZnO@C microrods.