Physico-chemical properties of the crystallization of biological macromolecules are of particular interest for an efficient way to get high-quality crystals. Concept and realization of a novel temperature-controlled microreactor to study these parameters is revealed. The characterization of the device is focussed on the temperature distribution across the reaction chamber, its long-term stability and accuracy as well as the regeneration of the surface inside the chamber after contamination with a hydrophilic protein (rGFP). We conclude that a microreactor for in situ observation of a temperature-controlled batch crystallization is in place.