a crystalline aluminum hydroxide having a uniform crystal structure which is free of defect deep in the particle not to mention in the surface layer or a crystalline aluminum hydroxide having a fairly uniform crystal structure which is not fully free of but has little defect deep in the particle and has a strong strength against the external force which crystalline aluminum hydroxide can be difficultly etched by a sodium hydroxide solution as described later in connection with fig4 fig4 is a graph illustrating the relationship between time and weight reduction represented by dissolution loss weight of raw material developed when a sample cr 40a as an example of difficultly etchable crystalline aluminum hydroxide for use in the crystallization of aluminutim hydroxide of the present invention and a crystalline aluminum hydroxide available from showa denko k k as an example of commercially available crystalline aluminum hydroxide are dissolved in a 100 g l caustic soda solution initial aluminum ion concentration 0 equivalent l at a temperature of 65 u00b0 c it can be seen in fig4 that the sample cr 40a of the present invention can be more difficultly etched by a caustic soda solution than the product available from showa denko k k the process for the purification of aluminuitm hydroxide of the present invention according to clause a will be further described hereinafter in the purification process according to clause a a mother liquor having a total caustic soda concentration of from.