A new type of water-based lubrication additive — colloidal polystyrene-carbon nanotubes (PSt-CNTs) has been prepared. Transmission electron microscope shows that the PSt-CNT colloids are tubes with tiny balls in nanometer scale. Four-ball test results indicate that both the load-carrying capacity and anti-wear of the colloidal PSt-CNTs are much superior to those colloidal PSt owing to the additive reinforced by CNTs. The optimum colloidal PSt-CNT content is 1.0 wt.%. The worn surfaces were analyzed using scanning electron microscope. Finally its lubrication mechanism was speculated preliminarily.