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 $0.1{sim}0.3{mu}m$ width and the two distinctly different transformation sequences of retained austenite, i) retained austenite${ ightarrow}$martensite and ii) retained austenite${ ightarrow}$deformation twin${ ightarrow}$martensite were revealed. The strength-elongation combination was increased with increasing the holdig time at low temperatures ($625^{circ}C$) but decreased abruptly with increasing holding time at high temperatures ($675^{circ}C$), owing to the lowering of ductility. The strength-elongation combination and TRIP effect was lower in tensile deformation in the range of $100{sim}250^{circ}C$ than room temperature. The tensile strengh and elongation of a reverse transformed steels with addition of Ti or Nb was 93kg/, 40% respectively, which is higher over 10% of strength without ductility loss than in 0.15%C-6%Mn steels.