Lanthanum hydroxide does not react much with alkaline substances, however is slightly soluble in acidic solution. In temperatures above 330 °C it decomposes into lanthanum oxide hydroxide (LaOOH), which upon further heating decomposes into lanthanum oxide ():
:  LaOOH
:2 LaOOH  
Lanthanum hydroxide crystallizes in the hexagonal crystal system. Each lanthanum ion in the crystal structure is surrounded by nine hydroxide ions in a tricapped trigonal prism.