This essay is about the crystallization of proteins. Since the first published observation of crystallizing proteins about 160 years ago, protein crystals growth has developed into an extensive research field with many applications, for instance in the pharmaceutical industry. Nowadays, different fermentation, purification processes and recombinant technology produce potential protein drugs at acceptable cost which can be useful in various diseases through various routes like oral, transdermal, nasal, pulmonary, ocular, buccal, and rectal. In this report, we focus on the continuous crystallization of proteins in a tubular plug-flow crystallizer. A solution of lysozyme from chicken egg was mixed with a crystallization solution and both of them went through three water baths at different temperatures along 13 meters of a silicone pipe. The different temperature of each water bath allows both nucleation and crystal growth, main steps in crystallization. The formed crystals are transported by air bubbles through the pipe to avoid the obstruction of the pipe. Through the experiments, we have varied many parameters such as the temperature, the flow rate, the amount of Ionic Liquid in the crystallization solution or even the type of reactor (batch or continuous) to compare the yield in different crystallization conditions, as well as the crystal shape and the solubility. Grado en Ingeniería Química