Abstract: Transmission electron microscopy (TEM) and nanobeam EDS technique were used to investigate the strain induced precipitation behavior during relaxation process after deformation in the non-recrystallization temperature range of a ultra-low carbon steel containing Nb, Ti and Mo. The experiment results indicate that after 30% predeformation at 850℃ and 900℃, two kinds of precipitates, combination of Nb and Ti and a few pure Nb, occur in the steel during isothermal holding. The atomic ratio of Nb to Ti in particles increased and pure Nb particles disappeared with the relaxation extended. After longer holding, some Nb and Ti atoms in the lattice sites of the precipitates were replaced by Mo atoms. The content of Mo in the precipitates rose with the relaxation time increased. The shape of the precipitates is mainly irregular and the density and average size of precipitates are related to deformation temperature and relaxation time.