Provided is a method for preparing plate-like ultrafine particles of flaky graphite having an average graphite plate diameter of 3-5 μm and a graphite plate thickness of 20-60 nm, including: grinding natural flaky graphite to control the particle size to 5-15 μm; dipping the ground flaky graphite into an aqueous solution containing an acid and an oxidizing agent, followed by washing and drying, to form a graphite intercalation compound in the ground flaky graphite; carrying out gasification of the graphite intercalation compound via low-temperature heat treatment to expand the flaky graphite to 20-30%; and carrying out wet grinding of the expanded flaky graphite at a slurry concentration of 20-28 wt %.The ultrafine particles of flaky graphite disclosed herein have a narrow particle size distribution, and maintain unique properties of flaky graphite due to the lack of interlayer collapse in flaky graphite particles.