Developing all-pH and efficient non-noble-metal electrocatalysts for the hydrogen evolution reaction (HER) remains a great challenge in science nowadays. In this work, carbon nanofiber (CNF)@CoS2 hybrids with a hierarchical core/sheath structure have been successfully fabricated via a combination of electrospinning and hydrothermal methods for use as HER electrocatalysts under all-pH media. The CoS2 nanoparticles are uniformly attached onto the three-dimensional (3D) CNF framework, and have different morphologies on adjusting the concentration of the Co and S precursors. This shows that the morphology of the electrocatalytically active CoS2 has a great impact on the HER performance, which can be attributed to the difference in the exposure of the effective catalytic sites. Moreover, the CNF@CoS2 hybrids distinctly exhibit superior HER activities compared to that of pure CoS2 agglomerates, which highlights the importance of the 3D carrier with a nanostructure to increase the number of exposed electrocatalytic sites. When applied as electrocatalysts operating at all-pH values, the CNF@CoS2 hybrids exhibit remarkable HER properties, with a low onset potential of -40 mV, a small Tafel slope of 66.8 mV per decade and a large current density (10.0 mA cm(-2) at eta = 110 mV) in acid medium, along with a low onset potential of -130 mV in both alkaline and neutral conditions. Apart from the facile preparation of an efficient all-pH electrocatalyst, this work highlights the impacts of morphology and nanostructure of the catalyst on the HER activity, which is universally applicable in the field of catalysis.