Abstract: Nano-sized barium sulfate has a small particle size，large specific surface area，and is easy to aggregate.So the dispersion behavior of nano-sized barium sulfate in liquid medium has been studied.The influence of pH，dispersant type， dosage of dispersing agent，dispersing medium，and ultrasonic time on the dispersing effect of nano-sized barium sulfate has been investigated.Thus the best dispersion conditions of nano-sized barium sulfate have been determined.Namely，using water as the liquid medium，pH=10，mass fraction of polyacrylic acid sodium is 5%，ultrasonic time is 15 min，the sedimentation height of nano-sized barium sulfate is 8.9 cm，the diameter is 61.79 nm，and the zeta value is -38.6 mV；or using dimethyl sulfoxide as the liquid medium，pH=7，ultrasonic time is 15 min，the precipitation height of the nano-sized barium sulfate is 9.7 cm，the diameter is 89.4 nm，and the zeta value is 22.3 mV.Under those conditions a good dispersion effect can be achieved.

Key words: nano-sized barium sulfate, liquid medium, dispersion