Active and stable electrocatalysts for the hydrogen evolution reaction (HER) are highly desirable for hydrogen production. Herein, the cuboid-like platinum nanocrystals (Pt-CNSs) are achieved through a facile L-lysine-assisted hydrothermal reduction method. Then, reduced graphene oxide (RGO) supported Pt-CNSs (Pt-CNSs/RGO) nanohybrids are obtained through the self-assemble of Pt-CNSs on graphene oxide (GO) and followed by NaBH4 reduction. The resulting Pt-CNSs/RGO nanohybrids are characterized by transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, thermogravimetric analysis and Raman, showing that the well-defined Pt-CNSs with 5.8 nm length and 3.0 nm width are uniformly and firmly attached on the RGO surface. Electrochemical tests demonstrate that Pt-CNSs/RGO nanohybrids have superior electrocatalytic activity and stability for the HER than pure Pt-CNSs, demonstrating RGO is an excellent cathode support materials for Pt-CNSs. Meanwhile, the present results indicate that the as-prepared Pt-CNSs/RGO nanohybrids have great potential application in HER. (C) 2015 Elsevier B.V. All rights reserved.