To obtain an aluminum hydroxide able to provide a resin composition when filling to a thermoplastic resin, manifesting excellent flame retardance free from derogation of excellent surface properties and mechanical strength without using other auxiliary flame retardant by grinding a specific aluminum hydroxide.

This aluminum hydroxide contains less than 0.3wt.% of Na expressed in terms of Na2O, average secondary particle size ≤10μm and manifests melt-flow rate of 0.55/10min when filling 150 pts.wt. of this aluminum hydroxide to 100 pts.wt. of a thermoplastic resin having melt-flow rate of 0.8/10min. This aluminum compound is obtained by grinding the ungrounded aluminum compound obained by Bayer's process containing less than 0.3wt.% of Na expressed in terms of Na2O, average primary particle size 0.5-60μm, average secondary particle size 0.5-60μm, is grounded with a volume grinding machine to the extent that the average secondary particle size is decreased to 10-90%, then the surface is crashed by trituration, etc.