Abstract: The transformation behavior of Nb-bearing microalloyed low carbon steel during continuous cooling with deformation at different temperatures was investigated by means of Gleeble-1500 thermomechanical simulator. The continuous cooling transformation (CCT) curves under deformed and undeformed conditions were obtained by way of thermal dilation and metallography. The influence of deformation parameters on microstructure was analyzed. The results showed that the transformation of pearlite is accelerated through high-temperature deformation, and transformation range of ferrite is reduced when deformed at the temperature above 950°C. In view of the starting transformation temperature, the bainite transformation is extended when deformed at 950°C. At the same deformation temperature, bainite amount decreases but proeutectoid ferrite amount increases with the increasing deformation amount. The formation of high-temperature equiaxed ferrite is accelerated and bainite transformation retarded when deformed at the temperature below 900°C.