We report for the first time ultrafine Ru nanoclusters (NCs) anchored on thin reduced graphene oxide (rGO) via introduction of the macrocyclic compound cucurbit[6]uril (CB[6]). The nanocomposite exhibits a comparable or better HER performance compared to Pt/C in acidic, alkaline as well as neutral media, which greatly broadens its application in different types of electrolyzers.