The development of highly efficient and durable catalysts for production and storage of clean energy remains a formidable challenge. Herein, a bifunctional electrocatalyst composed of ultrasmall ruthenium nanoparticles confined within a hollow nitrogen-doped carbon spheres (Ru/HNCS) was designed and synthesized through the pyrolysis of Ru³⁺ coordinated polydopamine layers. The as-synthesized Ru/HNCS with Ru content even below 0.1 wt% exhibited excellent catalytic activities towards both hydrogen production and oxygen reduction. When catalyzing hydrogen evolution reaction, a low overpotential of 39 mV was sufficiently to achieve the current density of 10 mA cm⁻² in acidic media and the corresponding Tafel slope was only 30 mV dec⁻¹. Furthermore, Ru/HNCS also exhibited outstanding oxygen reduction reaction activity with a half-potential of 0.72 V and an onset potential of 0.83 V, as well as high stability and palmary anti-poisoning capability for methanol in basic electrolyte. This Ru/HNCS might be a promising alternative to Pt-based electrocatalysts in energy conversion and storage.