Thermites prepared from nanoparticles are currently the subject of growing interest due to their increased performances compared to classical micrometer-sized thermites. Here, we studied the combustion behavior of energetic composite composed of Al and chromium (III) oxide (Cr2O3) as function of the oxide particle size. Homogeneous composites were prepared by mixing Al nanoparticles (Φ≈50 nm) with Cr2O3 micro- and nanoparticles (Φ≈20 nm), respectively, in hexane solution. The dried Cr2O3/Al composite powders were ignited by using a CO2 laser beam. The use of nanosized Cr2O3 particles incontestably improves the energetic performances of the Al/Cr2O3 thermite since the ignition delay time was shortened by a factor 3.5 (16±2 vs 54±4 ms) and the combustion rate (340±10 mm s−1) was significantly accelerated in contrast to those reported until now. Interestingly, the sensitivity to friction of the Al-based thermites formulated from Cr2O3 is two orders of magnitude lower than the thermite prepared from other metal oxide nanoparticles (MnO2, WO3). Finally, our study shows that the decrease of Cr2O3 particle size has an interesting and beneficial effect on the energetic properties of Cr2O3/Al thermites and appears as an alternative to tune the properties of these energetic materials.