In the sea water desalination process, brine is produced as a byproduct. Brine contains several resources which are various valuable ion materials in high concentration. If the sea water desalination process is integrated with a resource recovery process, a reduction in environmental load and production of valuable resources can be achieved. Mg2+ ion is the second most abundant ion in sea water. However, the development of a Mg2+ ion recovery method is not sufficient. The Mg2+ recovering method in magnesium hydroxide (MH) form from brine has been studied. Brine and bittern are produced when the sea water desalination process is integrated with the resource recovery process. When MH is recovered from concentrated sea water, two kinds of raw resource materials, i.e. brine and bittern, can be considered. However, the MH recovery process using brine as a raw resource material is not compared with the recovery process using bittern. This is because there is almost no fundamental data of MH crystals for process comparison, and MH crystals are produced as ultra-fine particles. Therefore, the purpose of this present study is to obtain the fundamental data for development of the MH recovery process in an integrated process. In particular, the prevention method of ultra-fine MH crystal deposition is investigated, and the yield and crystallinity of MH crystals are compared. It is clear that the yield and crystallinity of MH crystals are strongly dependent on temperature and the kind of raw resource material. These results show a strategy for improvement in process efficiency when MH crystals are recovered from the sea water desalination process.