Provided is an initial break-in lubricant composition capable of easily and economically reducing the coefficient of friction of a sliding portion. The initial break-in lubricant composition includes an organic dispersion medium and nanocarbon particles in a quantity from 0.1 to 2000 ppm by mass. The nanocarbon particles are preferably particles of one or more nanocarbon material(s) selected from the group consisting of: nanodiamonds, fullerenes, graphene oxide, nanographite, carbon nanotubes, carbon nanofilaments, onion-like carbon, diamond-like carbon, amorphous carbon, carbon black, carbon nanohorns, and carbon nanocoils.