Rational design and controllable synthesis of visible-light-responsive photocatalysts that exhibit both good hydrogen-producing efficiency and stability in the water splitting reaction are undoubtedly a challenge. Here we report an integrated CdS nanorod/oxygen-terminated Ti₃C₂T_x MXene nanosheet heterojunction with a high catalytic hydrogen evolution reaction (HER) activity. By incorporating one-dimensional (1D) CdS nanorods onto annealed ultrathin two-dimensional (2D) MXene nanoshees, the mixed-dimensional 1D/2D heterojunction achieved a hydrogen-evolving rate of 8.87 mmol × g^-1 × h^-1, much higher than that of bulk CdS and CdS/unmodified MXene hybrid catalysts. The enhanced HER activity and stability of the designed heterojunction catalyst are attributed to the presence of oxygen-containing terminal groups on the surface of thermally treated Ti₃C₂T_x MXene, extended light absorption spectra as well as the precisely-constructed intimate Schottky contact, implying an accelerated interfacial charge transfer and efficient, long-term photocatalytic hydrogen production performance. The results demonstrate that oxygen-terminated 2D MXene can be well utilized as a functional platform for the development of novel heterojunctioned photocatalysts.