MgO-C refractory was prepared by taking high quality fused magnesia, silicon powder, and flake graphite as raw materials, liquid calcium lignosulfonate with the concentration of 1.25g/mL was used as the binder. Then the samples were sintered under N₂ atmosphere via two-stage sintered process that a low-temperature stage is with 1350℃ for 2h and a high-temperature stage is with 1450℃ for 2h, 3h, and 4h, respectively. The effects of keeping warm time on phase compositions, microstructure, and conventional physical properties of MgO-C refractory are investigated. The phase composition of fired samples is analyzed by X-Ray diffraction. The microstructure is analyzed by scanning electron microscope. The conventional physical property is characterized by apparent porosity, bulk density, and compression. The results show that there are no evidently differences on the phase compositions and the size of SiC and α-Si₃N₄ whisker formed through the in-situ formation with the increase of keeping warm time from 2h to 3h. With the increase of keeping warm time to 4h, the silicon phase disappeared and the sizes of SiC and α-Si₃N₄ whisker have obviously increased. For the conventional physical performances, with the increase of keeping warm time from 2h to 4h, the formation of CO_(g) and SiO_(g) is increasing, which lead to a increase of apparent porosity and a decrease of bulk density and compression strength.