A novel liquid droplet generator, or atomizer, capable of generating either monodisperse droplet streams or a polydisperse spray, has been characterized using phase‐Doppler anemometry and two visualization techniques. The atomizer consists of a piezoelectric driver in a circular housing with an orifice plate across the end of the housing. Unlike conventional droplet generators or atomizers, this device directly induces a high‐amplitude velocity perturbation of the liquid jet. Orifice plates with a circular hole (diameter: 34 or 98 &mgr;m) or a rectangular hole (527×31 &mgr;m2) were used. In the low‐power mode, the atomizer with a circular orifice generated a stream of monodisperse water droplets with a diameter 1.5 to 3.4 times the jet diameter and a separation 2.3 to 26 times the jet diameter at 10 to 68 kHz. Droplets smaller than the minimum size predicted by Rayleigh’s criterion can be generated with an increased modulation power. The droplet velocity can be adjusted in a wide range (4 to 26 m/s), and a high Reynolds number (∼250) can be attained. In the high‐power mode, the atomizer produced a polydisperse water spray with a Sauter mean diameter less than half the jet (equivalent) diameter. The rectangular orifice required significantly less driving power to generate a spray. This atomizer is suitable for both fundamental studies and practical applications.