Al-SiC nanocomposites were fabricated by powder metallurgy route through mechanical milling and hot extrusion processes. Microstructure studies of as extruded billets revealed a fine distribution of nanometric reinforcements in the submicron and ultrafine grains of the aluminum matrix. Hot deformation behavior of the nanocomposites was studied by uniaxial compression test in temperature range of 350-500 oC and at strain rates of 0.005 to 0.5. The true stress- true strain curves exhibit a peak stress at a critical strain and then a dynamic flow softening. The flow stress decreased with increasing deformation temperatures and/or decreasing strain rates. The effect of nanometric inclusions on the activation energy of the hot deformation process was elaborated by the Zener-Hollomon parameter. It is shown that the reinforcing nanoparticles remarkably decreases the activation energy due to their pinning effect on grain boundaries and dislocation glide. The mechanisms of hot deformation of P/M nanocomposites are explained.