Effect of thermomechanical and magnetic treatment on creep characteristics of advanced heat resistant ferritic steels for USC power plants has been investigated to explore fundamental guiding principles for improving creep rupture strength at elevated temperatures over 873K. A model steel with a composition of Fe-0.08C-9Cr-3.3W-3Co-0.2V-0.05Nb-0.05N-0.005B-0.3Si-0.5Mn (in mass%) has been prepared by vacuum induction melting. Creep tests and microstructural observations were performed on the thermomechanical and magnetic treated specimen after tempering. New thermomechanical treatment without magnetic field showed some improvement in creep strength comparing with ordinally normalized and tempered specimen. Further improvement was observed in the specimen that had been exposed to a magnetic field during transformation to martensite. From the results of microstructural observation, it was found that the finely distributed precipitates such as MX and M23C6 caused this improvement. And it was suggested that the magnetic treatment at martensitic transformation increase the precipitation sites during tempering, resulting in increase the amount and prevent the growth of the precipitations.