Electrocatalytic nitrogen reduction reaction (NRR) is a green and sustainable strategy for artificial nitrogen fixation but remains a significant challenge because of the lack of high-performance electrocatalysts. In this study, flower-like hollow MoSe2 nanospheres as efficient earth-abundant NRR electrocatalysts with a high faradaic efficiency of 14.2% and an ammonia yield of 11.2 mu g h(-1) mg(cat.)(-1) at ambient conditions were prepared. Such excellent NRR activity can be attributed to the higher specific surface area, more active sites, and longer N-2 retention time within the shells because of the design of the hollow structure. Density functional theory calculations were performed to further understand the catalytic mechanism involved. This work demonstrates the feasibility of transition-metal selenides as NRR electrocatalysts and suggests an electrocatalyst materials structure design for efficient electrochemical nitrogen fixation.