In this study, the foaming behavior of metal matrix composites (MMCs) containing micron- and nano-sized TiB2 particles was compared. Foaming was achieved by adding blowing agent into the MMC melt at 670 °C. Macrostructural and microstructural characterization of the foams were performed by using X-ray tomography and scanning electron microscopy. Quasi-static compression tests were conducted to analyze the mechanical behavior of the foams. Foams stabilized by nanoparticles showed higher expansion than those stabilized by micron-sized particles indicating a better stabilization by nanoparticles. The foams containing nanoparticles also exhibited better mechanical properties. This is mainly due to the presence of nanoparticles in the microstructure. © 2017 Elsevier B.V.