Abstract <p>Effect of 28 different dispersion media on the efficiency of liquid-phase ultrasonic exfoliation of hexagonal boron nitride has been investigated. The data on the coefficient of light absorption by the suspensions have been used to determine the Hansen solubility parameters for boron nitride nanosheets. The optimal ethanol content in a water/ethanol system has been found. The effects of the dispersion medium composition, exfoliation time, and initial concentration of hexagonal boron nitride on the efficiency of ultrasonic exfoliation and structural characteristics of the obtained nanosheets have been analyzed. The use of water/ethanol mixtures with ethanol contents of 33.3 and 66.7 vol % at an initial boron nitride concentration of 10 g/L has made it possible to reach 8 and 10% yields of nanosheets, respectively. The lateral sizes of the sheets are 630–680&#xa0;nm and their thicknesses are below 25 nm. The conditions have been described for manufacturing suspensions with very high concentrations of boron nitride nanosheets equal to 3.3 g/L. Due to the high yield and the high aspect ratio (25 and higher) of the nanosheets, the process can be successfully used to prepare fillers and additives for composite materials, as well as suspensions for printing and film technologies.</p>