The use of graphene and multi-walled carbon nanotubes (MWCNTs) additives as lubricants has received considerable interest because of their excellent mechanical and frictional properties. Given their structural differences, both carbon nano-additives are expected to have different synergistic effects at various conditions (from boundary to mixed lubrication). For applications in space, the tribological properties of graphene and MWCNTs additives in diamond-like carbon/ionic liquids hybrid films in different lubricating states at high vacuum were compared. The wear surfaces, transfer films, wear debris, and microstructures of the hybrid films were analyzed via Raman spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. The results showed that MWCNTs and graphene present the different nano-scale tribological mechanisms and produce different lubricating effect on the hybrid films at different lubricating states. (C) 2014 Elsevier Ltd. All rights reserved.