Abstract : Silica aerogels of desired shape have been elaborated to perform critical stress intensity factors evaluations as a function of the density. The fracture toughness of aerogels is measured usin SENB technique in three-point bending. KIC varies in the range 0.8 to 4.8 KPa.m1/2. For aerogels whose bulk density ranges between 0.1 and 0.35 g/cm3 the analysis of the obtained results suggests that KIC varies as ρ1.6±0.2. The fracture energy variation and the critical size flaw derived from toughness, strength and Young's modulus are also presented and discussed.