Microdroplets have a wide extent of applications due to the related advantages, such as high throughput, compartmentalization with a deep control of the single volume. Herein, a microdroplet-based device for protein phase transition was displayed. In doing so, biphasic droplets with tunable internal structures and phase with near-equilibrium drop-in-drop morphology were created. The protein phase was controlled by modulating the composition, and the flow velocities. The microfluidic device allowed investigating the morphology of the protein and the phase transition from gelation to crystallization, via the formation of the magma-unstable phase. The creation of droplets with tunable spatial heterogeneity could be exploited in biochemical investigations. (C) 2015 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.