The effect of Cr 2 O 3 particle size on the densification of magnesia refractories was investigated. Magnesia grains (<45μm) were mixed with 2wt% of micro-Cr 2 O 3 (2μm) and nano-Cr 2 O 3 particles (10–20nm) and sintered at 850–1450°C, for 5h in air. The progress of the densification and phase evolution of samples was studied with the support of X-ray diffraction phase analysis (XRD), Fourier transformer infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). It was shown that the densification of magnesia was enhanced by reducing the particle size of the added chromia to the range of 20nm. According to the phase analysis results, the higher dissolution rate of Cr 2 O 3 in MgO in the MgO–Cr 2 O 3 system was responsible for the faster densification of nano-Cr 2 O 3 containing mixes.