Unburned magnesium aluminate spinel refractories were prepared using sintered magnesium aluminate spinel as the main raw material, phenolic resin as the binder, aluminum powder (2%, 4%, and 6% by mass) and silicon powder (when Al powder addition is 4%, Si powder addition varies: 1% and 2%, by mass) as additives. The effects of the Al powder and Si powder additions on the properties and microstructure of the refractories heat treated at different temperatures (1 000, 1 400, and 1 600 ℃ for 3 h) were studied. The results show that the Al powder addition can greatly enhance the cold modulus of rupture of the samples fired at 1 000 or 1 400 ℃, and meanwhile AlN reinforcement phase forms in the matrix, which greatly improves the hot modulus of rupture of the samples at 1 400 ℃; however, the heat treatment at 1 600 ℃ has little influence on the strength; the addition of Al powder and Si powder results in the formation of low melting point phases, greatly reducing the hot modulus of rupture. However, the low melting point phases promote sintering, which enhances the density and the cold modulus of rupture, and decreases the volume change during heating. The samples added with Al and Si all have higher cold modulus of rupture than those added with Al powder only.