This study aims to provide the basic knowledge for furnace refractory design by investigating refractory property changes occurred in a hydrogen atmosphere. Since refractory bricks are thermodynamically stable in a hydrogen atmosphere at 1 100 °C, we tried to find out the minute changes. In this experiment, a refractory brick was prepared by andalusite, mullite chamotte, and clay as raw materials and heated to 1 100 °C in a 100% hydrogen atmosphere for 72 h. It was found that the strength of the brick was decreased and the color was changed to black by the reduction of impurities. And in addition, this study covered research on the slaking risk of MgO raw materials because the minimum temperature is expected to 400 °C in fluidized reduction furnaces unlike shaft furnaces.