The optical (refractive indices, piezooptic coefficients, optical damage thresholds and the transmission spectra) and the elastic properties of the borate crystals (BaB2O4, Li2B4O7 and CsLiB6O10) are investigated. The results of measurements for the velocity of longitudinal and transverse ultrasonic waves of the borate crystals are presented. The components of the elastic matrix Cmn of these crystals are calculated on the basis of the ultrasonic velocity measurements. Using the determined values of the refractive, elastic and elastooptic tensor components, we have calculated the largest values of the acoustooptic figure of merit M2.