Transition-metal chalcogenides with hollow nanostructure,especially cobalt sulfides,are considered as the most promising non-precious metal catalysts for oxygen evolution reaction.However,it is difficult to synthesize oxygen-containing cobalt sulphides with hollow structure due to the different physical/chemical properties between metal sulfides and metal cobalts.Herein,we report a novel oxygen-containing amorphous cobalt sulfide ball-in-ball hollow spheres (Co-S-O BBHS) synthesized by an anion exchange method.Taking advantage of the ball-in-ball hollow structure,the amorphous Co-S-O BBHS shows superior oxygen evolution reaction (OER) electrocatalytic performance with a low overpotential of 285 mV at 10 mA/cm2,small Tafel slope of 49.67 mY/dec,high Faraday efficiency of 96％,and satisfied durability.Experiments and DFT calculations demonstrate that the introduction of oxygen and sulfur modulates the electronic structure of Co-S-O BBHS,thus enhancing the adsorption of *O (adsorbed O species on catalyst surface) intermediate,which greatly boosts the catalytic activity towards OER.This work provides a new strategy for controllable synthesis of complex hollow structures of transition-metal chalcogenides for OER.