The effect of aging on the mechanical properties and microstructures of a new ZG12Cr9 MolColNiVNbNB ferritic heat resistant steel was investigated in this work to satisfy the high steam parameters of the ultra-supercritical power plant.The results show that the main precipitates during aging are Fe(Cr,Mo)_(23)C_6,V(Nb)C,and(Fe_2Mo) Laves in the steel.The amounts of the precipitated phases increase during aging,and correspondingly,the morphologies of phases are similar to be round.Fe(Cr,Mo)_(23)C_6 appears along boundaries and grows with increasing temperature.In addition,it is revealed that the martensitic laths are coarsened and eventually happen to be polygonization.The hardness and strength decrease gradually,whereas the plasticity of the steel increases.What’s more,the hardness of this steel after creep is similar to that of other 9%-12%Cr ferritic steels.Thus,ZG12Cr9 MolColNiVNbNB can be used in the project. The effect of aging on the mechanical properties and microstructures of a new ZG12Cr9 MolColNiVNbNB ferritic heat resistant steel was investigated in this work to satisfy the high steam parameters of the ultra-supercritical power plant. The results show that the main precipitates during aging are Fe ( Cr, Mo) _ (23) C_6, V (Nb) C, and (Fe_2Mo) Laves in the steel. The amounts of the precipitated phases increase during aging, and correspondingly, the morphologies are similar to be round. Cr, Mo) _ (23) C_6 appears along boundaries and grows with increasing temperature. In addition, it is revealed that the martensitic laths are coarsened and eventually happen to be polygonization. Hardness and strength decrease gradually, but the plasticity of the steel increases.What’s more, the hardness of this steel after creep is similar to that of other 9% -12% Cr ferritic steels.Thus, ZG12Cr9 MolColNiVNbNB can be used in the project.