Abstract In this paper, we report the trapping, transportation and separation of small particles in liquid by an acoustic needle which is driven by a sandwich type ultrasonic transducer. After analyzing the mechanism of trapping small particles by the tip of the vibrating needle, the characteristics of trapping, transportation and separation of small particles such as Flying Color seeds, grass seeds and shrimp eggs are presented. The trapping capability increases with the increase of sound pressure around the tip, and becomes saturated when the sound pressure is too large. It may also be affected by the viscosity of fluid. A large viscosity reduces the trapping capability. The trapped particles can be transported in water by moving the needle and the particle loss during the transportation may be avoided by using a strong enough vibration. The acoustic needle can also separate different particles in water by the difference in their densities.