Twinning induced plasticity (TWIP) steels with excellent strength and elongation properties are expected to be the next generation of automotive high-strength steels. The present work investigates endogenous inclusions formed in Fe–25Mn–3Si–3Al TWIP steels in laboratorial ingot, mold casting after AOD steelmaking and electroslag remelting (ESR) process at industrial plant, respectively. The research shows that AlN and Al2O3 inclusions are found as dominating inclusions, and most of them are AlN, but the number, distribution, size shape of inclusions have big differences in different metallurgical processes. The AlN inclusions in laboratorial ingot mainly present cluster states and have larger size, but after AOD or ESR process most of AlN inclusions are uniformly distributed, this would reduce harm to steel quality. From the point of view of thermodynamics, the research finds that the generation of AlN inclusions in Fe–25Mn–3Si–3Al steels is different from that of most of other high-Al steels or Al-killed steels, because many publications reported that the precipitation of AlN inclusions took place at solidifying front or solid phase, but AlN inclusions formed in Fe–25Mn–3Si–3Al steels generate in liquid steel, and related experimental results prove this point.