To obtain an efficient and low-cost adsorbent for the Sb(V) removal in Sb(V)-contaminated water, a novel composite manganese oxide/oxyhydroxide (CMO) was synthesized by a simple hydrothermal synthesis method. The synthesized adsorbent was characterized via scanning electron microscopy, X-ray diffraction, transmission electron microscopy, Brunauer-Emmett-Teller surface area, Fourier transform infrared, and X-ray photoelectron spectroscopy analyses. The results revealed that the as-prepared CMO adsorbent possessed a porous structure consisting of Mn3O4 nanoparticles and MnOOH nanorods. Batch experiments showed that the adsorption behaviours were well fitted by the Langmuir isotherm and the pseudo-second-order kinetic model, reaching the maximum adsorption capacity of 119.63 mg/g at 25 °C. The application of CMO adsorbent showed that the Sb(V) removal efficiency in 6.24 L Sb(V)-containing water with a concentration of 3.6 mg/L was more than 90%. The reusability of CMO adsorbent demonstrated that the Sb(V) removal efficiency was still more than 80% even after five times of regeneration. The adsorption mechanism for Sb(V) can be described as ligand exchange between hydroxyl groups on the adsorbent surface and hydroxyl groups in Sb(OH)6- molecules by forming inner-sphere complexes. Those results suggested that the CMO adsorbent can be considered as a potential adsorbent to remove Sb(V) from contaminated water.