The application of ultrasound during the batch-wise as well as continuous crystallization of lipid nanoparticles is reported. For the latter, a micro heat exchanger is modified, allowing the inline application of ultrasound to promote the -to- transformation of the lipid nanoparticles. Ultrasonication during batch crystallization is carried out in an ultrasonic bath. While for batch processing the application of ultrasound leads to an increase of the fraction of stable -polymorph according to differential scanning calorimetry measurements, no significant increase is found for continuous operation. This is a result of one or both of the following effects: The residence time in the continuous micro heat exchanger is approximately 1s and thus possibly too short for significant influences on the polymorphism or crystallization. Additionally, the ultrasound is induced indirectly to the product side and thus reduced.