Thermo-simulation test and transmission electron microscopy （TEM） have been used to investigate the interaction between the microalloying elements Nb and Mo within the precipitates during relaxation after austenite deformation of C-Ti-Mo steel and C-Nb-Mo steel. The experimental results demonstrated that the austenitic structure was preserved both in C-Ti-Mo steel and C-Nb-Mo steel even if they were relaxed for 1000 s after deformation at 850℃. The strainqnduced precipitate occurs in two kinds of steel. Through the energy spectrum analysis, it was found that the precipitates were Ti（C, N） and Mo-bearing Nb（C, N） respectively and there exists a strong affinity of Mo for Nb with in the precipitates. Mo atoms would enter the lattice of Nb（C, N） particles probably after Nb（C, N） formation.
