In this article, recent advances in the fundamental research in the protein crystallization under high pressure were reviewed. Pressure is expected to be an important parameter to control protein crystallization, since hydrostatic pressure affects the whole system uniformly and can be changed very rapidly. So far, a lot of studies of protein crystallization under high pressure have been done, some less systematic than others. We have particularly focused on fundamental aspects (the solubility and the crystal growth kinetics) of protein crystallization under high pressure. The studies reviewed contribute significantly to high-pressure crystallography and high-pressure protein science.