Abstract: Water was chosen as disperse medium and nano-sized CaCO₃ was dispersed through adding dispersants and ultrasonic treatment.The dispersion state was indicated through testing the transmittance and zeta potential of the dispersion and particle size of nano-sized CaCO₃.By comparing the dispersion states when sodium hexametaphosphate(SHMP),sodium polyphosphate(SPP),sodium dodecylbenzenesulfate(SDBS) were used as dispersants respectively,SDBS was proved to be the best for dispersion of nano-sized CaCO₃in water.The influence of the amount of dispersant,pH value and the time of ultrasonic treatment on the dispersion state was discussed.The optimum dispersion state might be achieved when the amount of SDBS was 0.14% with pH=8.5 and ultrasonic treatment for 5 minutes.