Cooling crystallization of beta-sitosterol that is a kind of phytosterol was carried out, where a water-immiscible solvent hexane containing a ppm level of water was used as a solvent. The initial ratio of water and beta-sitosterol concentration adopted in this work was 330110, 1315110 and 645/20 ppm/(g/L), which corresponded to 0.51, 2.0, and 0.50 in water/beta-sitosterol mole ratio, respectively. When the initial ratio of water and beta-sitosterol concentration was 1315/10 ppm/(g/L), thin plate-like crystals were precipitated and were identified as the monohydrate crystals of beta-sitosterol. On the other hand, when the initial ratio of water and beta-sitosterol concentration was 645/20 ppm/(g/L), needle-like crystals of hemihydrate were precipitated. This result meant that the ppm level of water plays an important role for the pseudo-polymorphism. Since the crystal structure of beta-sitosterol hemihydrate had never been reported, we determined it by a single crystal XRD analysis.