The TRIP behavior in tensile deformation of retained austenite formed by reverse transformation treatment in 0.15%C-6%Mn-(Ti, Nb) steels has been investigated. The shape of retained austenite was almost a fine lath type with 0.1∼0.3㎛ width and the two distinctly different transformation sequences of retained austenite, i) retained austenite→artensite and ii) retained austenite→deformation twin→martensite were revealed. The strength-elongation combination was increased with increasing the holdig time at low temperatures (625℃) but decreased abruptly with increasing holding time at high temperatures (675℃), owing to the lowering of ductility. The strength-elongation combination and TRIP effect was lower in tensile deformation in the range of 100∼250℃ than room temperature. The tensile strengh and elongation of a reverse transformed steels with addition of Ti or Nb was 93㎏/, 40% respectively, which is higher over 10% of strength without ductility loss than in 0.15 %C-6%Mn steels.