This work presents and discusses the anitwear characteristics of surface modified CuO nanoparticle suspensions in bio-based lubricant. 1.0 wt% unmodified as well as surface modified CuO nanoparticles (nominal size of 50 nm), were dispersed in base oil using an ultrasonic probe. Wear protection was evaluated by using Four-Ball Extreme Pressure (EP) testing and sliding wear tests. The scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) analysis of the worn surface shows that: surface modification helped to improve the dispersion stability of CuO nanoparticles and related suspension show high EP characteristics in terms of load wear index and low cylinder liner wear due to surface mending effect of nanoparticles.