Effect of Nb on microstructure and mechanical properties of chilled cast iron at room and elevated temperatures isstudied in this research. The results demonstrate that the cast structure and mechanical properties of chilled castiron at room and elevated temperatures are improved with the addition of trace amount of Nb. However, if Nb wasadded too much, the cast structure and mechanical properties of chilled cast iron would deteriorate. The suitablecontent of Nb in chilled cast iron is about 0.05% (mass fraction). Except the dissolution in the matrix of cast ironthe excessive Nb will form Nb-rich phases in three morphologies. Those are lumpy NbC, complicated strip-like phaseand compound with pearlite structure. Effect of Nb on microstructure and mechanical properties of chilled cast iron at room and elevated temperatures is found in this research. The results demonstrate that the cast structure and mechanical properties of chilled castiron at room and elevated temperatures are improved with the addition of trace amount of Nb However, if Nb wasadded too much, the cast structure and mechanical properties of chilled cast iron would deteriorate. The appropriate content of Nb in chilled cast iron is about 0.05% (mass fraction). Except the dissolution in the matrix of cast ironthe excessive Nb will form Nb-rich phases in three morphologies. Those are lumpy NbC, complicated strip-like phase and compound with pearlite structure.