Spark Plasma Sintering (SPS) has been recognized, in the recent past, as a very useful method to produce metal matrix composites with enhanced mechanical and wear properties. Obviously, the materials final properties are strongly related to the reinforcement types and percentages as well as to the processing parameters employed during synthesis. The present paper analyses the effect of the addition of 2wt% of Al2O3, SiO2 and carbon nanotubes (CNTs) on the mechanical and microstructural behavior of Al-based metal matrix composites produced via SPS. The results show that porosity and mechanical properties are strongly related to the reinforcement type. In particular a strong beneficial effect is revealed by Al2O3 nano particles and carbon nanotubes because of the optimal reinforcement dimensions.