An experimental study about the velocity, size and concentration of ultrasonic cavitation bubbles is presented. Ultrasound is provided from a 20 kHz horn dipping vertically into a liquid container. Using the laser phase-Doppler technique, cavitation bubble velocity and size distributions are obtained at various locations inside the ultrasound field. Axial and radial profiles of average bubble velocity, mean diameters and volumetric flow rate are presented. The influence of ultrasound power input is also investigated: it increases bubble velocity quasi-linearly and has more complex effect on bubbles diameter. The system investigated possesses similar hydrodynamic properties with typical turbulent circular jet flows.