A reinforcing aluminum-based filler which can be used for reinforcing diene rubber compositions intended for the manufacture of tires, comprising an aluminum (oxide-)hydroxide corresponding, with the exception of any impurities and the water of hydration, to the general formula (a and b being real numbers):the specific BET surface area of which is between 30 and 400 m2 / g, the average particle size (by mass) dw of which is between 20 and 400 nm and the disagglomeration rate, alpha, of which, measured via an ultrasound disagglomeration test at 100% power of a 600-watt ultrasonic probe, is greater than 5x10-3 mum-1 / s is provided. A rubber composition suitable for the manufacture of tires comprising said aluminum-based filler as reinforcing filler.