Abstract: Nanodiamond powder obtained by explosive detonation with an average particle size of 360nm was oxidized by an acid mixture containing concentrated H₂SO₄ (98%) and H₃NO₃ (70%) with a volume ratio of 3:1, then dispersed with sonication in a polyethylene glycol solution(PEG200), and finally irradiated with a 1 064 nm laser for 1 h to prepare a stable nanodiamond colloidal solution. TEM, XRD, FTIR, VSM and PL spectroscopy were used to characterize the properties of the nanodiamond particles, such as morphology, particle size, microstructure, luminescence and magnetic properties. Results show that the acid oxidation introduces surface functional groups on the nanodiamond powder, but there are still amorphous carbon and secondary aggregates in the stable nanodiamond suspension in PEG200 before the laser irradiation. Amorphous carbon is removed and the aggregates in the nanodiamond suspension are broken into primary nanoparticles of 5 nm with the laser irradiation. The well-dispersed nanodiamond colloid in PEG200 solution after laser irradiation shows strong ferromagnetism and a high concentration of CC and C—OH bonds that favors the formation of the stable colloidal solution.