Developing highly efficient and cost-effective electrocatalysts for oxygen evolution reaction (OER) is crucial for renewable energy storage technologies. Here, we synthesized hierarchical Co-based bimetallic sulfide nanostructures as an efficient electrocatalyst for OER. Ni3.5Co5.5S8 nanostructures were synthesized by solvothermal sulfurization and thermal annealing of pre-synthesized homogenous bimetallic metal-organic frameworks (MOFs). Electron microscopy studies revealed that the Ni3.5Co5.5S8 has hollow nanocage like morphology with thin nanosheets grown on the surface. In addition, Co9S8 hollow nanocages were also synthesized for comparative electrocatalytic evaluation with the Ni3.5Co5.5S8 nanosheet-assembled hollow nanocages (NAHNs). The Ni3.5Co5.5S8 NAHNs has exhibited a low over potential of 333 mV at the current density of 10 mA cm(-2) (1.563 V vs RHE) and Tafel slope of 48.5 mV dec(-1) for the oxygen evolution reaction in 1 M KOH. Benefitting from their structural merits, Ni3.5Co5.5S8 NAHNs manifest excellent OER electrocatalytic activity compared to most of the recently reported non-precious catalyst for OER. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.