Abstract: To investigate the effect of nano-Cr₂O₃ addition method on the resistance of magnesia-calcia bricks to low-basicity slag corrosion, magnesia-calcia bricks are fabricated with nano-Cr₂O₃ as an additive via three approaches: direct addition (MC), introduction as pre-synthesized fine powder (YMC) and introduction as pre-synthesized aggregate (CYMC). Their corrosion resistance is compared in a low-basicity CaO-SiO₂-MgO-Al₂O₃-Fe₂O₃ slag system. The results show that the CYMC sample exhibits the highest bulk density (approximately 3.10 g·cm^-3) and the lowest apparent porosity (approximately 9.01%), with mechanical strength at room temperature superior to those of YMC and MC. In static crucible corrosion tests, slag penetration depths of 0.92, 0.74 and 0.60 mm are measured for MC, YMC and CYMC, respectively, indicating a sequence of MC > YMC > CYMC. Microstructural analysis reveals that pre-synthesized (Mg,Ca)Cr₂O₄ spinel is uniformly distributed at grain boundaries, which reduces slag penetration along grain boundaries, inhibits the dissolution of MgO and CaO, and mitigates the reaction between free CaO and SiO₂ in the slag. In contrast, agglomeration is observed when nano-Cr₂O₃ is directly added and the formed spinel is distributed inhomogeneously. Microcracks and pores are thus induced, resulting in the poorest slag resistance. It is concluded that the introduction of nano-Cr₂O₃ as pre-synthesized aggregate significantly improves the densification and resistance of magnesia-calcia bricks to low-basicity slag corrosion.