Droplet microfluidics allows a higher degree of control over the crystallization conditions than conventional methodologies. To extend this approach, this work explores the synergistic effect of low-frequency pulsed ultrasound on lysozyme crystallization in microdroplets. Pulsed actuation allows control of the crystallization temperature, while the ultrasound effect significantly reduces the induction time and crystal size. Therefore, protein nucleation is enhanced by pulsed sonication without causing precipitation, resulting in uniform crystal size. Finally, the initial supersaturation ratio has a crucial contribution to the crystal size for silent experiments, while a threshold for induction time is observed in ultrasonic crystallization. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.