This paper presents results of the ultrasonic velocity measurements in the temperature range 291-303 K and absorption coefficient measurements in the frequency range 5-43 MHz and temperature range 0.15=<T-T c =<20 K in the benzonitrile-isooctane critical mixture. Ferrell and Bhattacharjee dynamic scaling theory which predicts a linear dependence between α c /f 2 and f - 1 . 0 6 was chosen for data analysis. This relation was confirmed by experimental data. The results of acoustic attenuation were also compared with the scaling function of Shiwa-Kawasaki mode-coupling theory, Kroll-Ruhland renormalization-group theory, and Ferrell-Bhattacharjee dynamic scaling theory.