A fine particle of aluminum hydroxide is disclosed, comprising a particulate aluminum hydroxide X having a specific surface area of 1.0 m2/g or less and a secondary particle size of 35 to 150 &mgr;m, a particulate aluminum hydroxide Y having a specific surface area of 1.0 m2/g or less and a secondary particle size of 10 to 35 &mgr;m and a particulate aluminum hydroxide Z having a specific area of 3.0 m2/g or less and a secondary particle size of 0.5 to 10 &mgr;m, in a compositional mass ratio falling in the area surrounded by four points of Point &agr;, Point &bgr;, Point &ggr; and Point &dgr; including the lines in the ternary composition diagram shown in FIG. 1. By this fine particle of aluminum hydroxide, a fine particle of aluminum hydroxide and a resin composition comprising the fine particle of aluminum hydroxide, which can be reduced in the viscosity at the filling in a resin and attain high filling and when filled in a thermosetting resin, can be shortened in the curing time, can be provided.