Antimony tin oxide (ATO) nanoparticles were prepared using co-precipitation with tin chloride and antimony chloride as the main raw materials. X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM) and ultraviolet-visible spectrophotometry were used to characterize the crystal structure, morphology and laser reflectivity. The effects of the pH value, co-precipitation reaction temperature, calcination temperature and calcination time on the laser reflectivity of ATO nanoparticles were studied. The results show that, compared with the undoped SnO2 powder, the reflectivity of a Sb-doped ATO powder at a laser wavelength of 1.06 µm is significantly reduced, and with an increase in the Sb doping, the reflectivity of the ATO powder at 1.06 µm first decreases and then increases. When the Sb/Sn molar ratio is 2/10, the reflectivity decreases to the lowest point, which is caused by the high concentration of Sb5+. ATO powders (Sb/Sn = 2/10) prepared at a titration-end-point pH of 2, co-precipitation temperature of 70 °C, calcination temperature of 800 °C and calcination time of 6 h have the lowest laser reflectivity at the laser wavelength of 1.06 µm, which is less than 0.02 %.