The effects of Ti-Nb microalloying on the microstructure and mechanical properties of an ultra-pure 30% Cr super ferritic stainless steel were studied by means of optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that the inclusions in the matrix of ultra-pure material are mainly composed of Cr-rich oxides with approximately size of 2~6 μm. With Ti-Nb addition, Cr-rich oxides are transformed into Ti-O-N-rich composite oxides with approximately size of 1~4 μm. Moreover, the nano-scale (Ti, Nb)(C, N) precipitations are formed in the matrix with Ti-Nb microalloying. It is worthy of noting that the strongly growth inclination of ferrite grain is the unique feature for the ultra-pure material during microstructure evolution. Ti-Nb microalloying can apparently refine the microstructure by weakening the migration rate of grain boundary, and it can also promote the room temperature strengthen and hardness. Meanwhile, the sensation of room temperature elongation of material on grain size is enhanced by Ti-Nb microalloying. In addition, Ti-Nb microalloying has the double effect on the impact toughness for the ultra-pure material. On the one hand, the toughness can be improved by refining the grains, on the other hand, brittle inclusions formed in matrix apparently deteriorate the toughness of ultra-pure material, especially for the toughness at low temperature。