Designing hierarchical nanostructures of earth-abundant electrocatalysts for enhanced overall water splitting performance is of great significance. Herein, Mo-doped Co(OH)₂ hierarchical nanotubes (Mo-Co(OH)₂ HNTs) assembled by cross-linked porous nanosheets are designed and synthesized through a sacrificial template strategy. Benefiting from the hierarchical structures based on porous nanosheets with void interior as well as modified electronic structure of higher intensity of Co³⁺ species by Mo⁶⁺ doping, the Mo-Co(OH)₂ HNTs demonstrate superior electrocatalytic performance, achieving an current density of 10 mA cm^-2 at the low overpotentials of 218 mV and 125 mV for oxygen and hydrogen evolution reactions, respectively. Furthermore, an overall water splitting cell was assembled with the Mo-Co(OH)₂ electrocatalyst as both the anode and cathode materials, which exhibits a driving voltage of as low as 1.62 V. The facile strategy presented in this work can be extended to the construction of various hollow/porous nanostructures with effective heteroatom doping to achieve low-cost, bifunctional and high-performance electrocatalysts for overall water splitting.