In this study, the effects of matrix microstructure of 2XXX Al-SiCw composites of the mechanical properties were analyzed. The used materials were powder metallurgy processed 2124 and 2009 aluminum composites reinforced with 15 volume percent SiC whiskers. Fracture parameter analyses and microstructural observations revealed that the improved fracture toughness of the 2009 Al-SiCw Composite, compared to the 2124 composite, was due to the increase in the critical microstructural distance ℓ when Mn-containing particles are absent. The 2009 composite was also heat treated in T4 and overaged conditions. The overaged 2009 composite had lower ductility and also much lower value of critical fracture strain compared to that of the T4 condition. Detailed fractographic analyses indicated that the most common form of damage was the cracking of SiC whiskers in the overaged condition and the decohesion of Al/SiCw interface in the T4 condition, respectively. The change of fracture mechanism can be explained by the increased load transfer to the whiskers in the overaged condition resulting in the whisker cracking and early failure during fracture process.