Two V–Ni microalloyed transformation-induced plasticity (TRIP) steels with different Ni content were designed and investigated. Transformed volume fraction of retained austenite as a function of tensile strain was measured using an X-ray stress apparatus aided by microelectronic universal testing machine and the evaluation of the stability of retained austenite was conducted. Precipitation of carbides during bainitic isothermal transformation was investigated using the technique of carbon extraction replica and transmission electron microscopy. X-ray diffraction was used to determine the volume fraction of retained austenite and its carbon content. In the present work, the effect of Ni addition on the stability of retained austenite and mechanical properties for TRIP steels was detailed.