There are provided a surface-modified nanodiamond exhibiting easy dispersibility in an organic solvent, an organic solvent dispersion thereof, and a method for producing the surface-modified nanodiamond. The surface-modified nanodiamond according to the present invention includes a nanodiamond, and a group bound to a particulate surface of the nanodiamond and represented by formula (1): —NHCOR   (1) R is an organic group having a carbon atom at a binding site with a neighboring carbonyl carbon atom indicated in the formula; and the left end, in the formula, of the group serves to form bonding to the nanodiamond. The nanodiamond is preferably a detonation nanodiamond or a high-temperature high-pressure nanodiamond.