In-situ magnesia-rich spinel fiber was formed resulting from the addition of ferro-cene into MgO-C refractory matrixes.The formation of in-situ spinel fiber was detected to start at 1300 ℃.The amount,diameter and length of the fibers increased with rising temperature.Ferrocene may have catalytic effects on the growth of the fibers in two aspects.First,the reaction between MgO and C and the decomposition of Al_4C_3 may be catalyzed at high temperature.Suitable concentration gaseous phase is then created for vapor-vapor reaction which could result in the in-situ formation of fibers.Second,Fe nanoparticle produced from ferrocene can act as catalytic droplets and catalyze the growth of the fibers.The fibers are formed via the vapor-liquid-solid and vapor-solid mechanisms.In terms of chemical thermodynamics,the partial pressure of CO and Mg(g)are found to play an im-portant role in the in-situ fibers formation.Different concentration of vapors affects the size,amount and composition of the fibers at different temperatures.The mechanical properties of MgO-C brick was found to be improved by ferrocene addition.