Anatase TiO2 quantum dots (QDs) with 3 nm particles were synthesized via a new synthetic route and showed narrow bandgap energy of 2.85 eV and good dispersibility in an aqueous system. This material exhibited significantly high photocatalytic activity for the degradation of methyl orange (MO). The photocatalytic activity of TiO2 QDs was 16‐fold higher than that of commercial P25 at an initial MO concentration of 50 mg L‐1 in the reaction system. At an MO concentration of 10 mg L‐1, it could almost be removed within 1 min. The high photocatalytic activity could be attributed to the low bandgap energy, large surface area, and good aqueous dispersibility of anatase TiO2 QDs.