The sedimentation velocity and its fluctuations were investigated for polystyrene microspheres with the diameter 3.6-32 mu m by high-frequency dynamic ultrasound scattering. A longitudinal broadband transducer centered at the nominal frequency 20 MHz was employed to probe the particle dynamics along the directions parallel and perpendicular to the sedimentation direction in highly turbid solutions. For the former case, the average sedimentation velocity and its variance were obtained since the direction of the scattering vector coincides with that of the particle displacement. Subsequently, the velocities were calculated to estimate the particle diameters. On the other hand, the velocity fluctuations can be solely determined when the wave propagation direction is normal to the gravity because the average displacement is zero. The velocity fluctuations were evaluated as a function of the sample position, and it was found that the significant decrease in the velocity fluctuations near the two cell walls was observed. The resonance scattering could have an additional role, exclusive for the large particles. Analysis on particle sizing was also attempted from the measurements of the horizontal velocity fluctuations.