Nano-structured bainite possesses an excellent mechanical strength and satisfactory ductility owing to nano-scale microstructure comprising of bainitic ferrite and retained austenite present in form of blocky and film type austenite. A significant change in the prior austenite grain size can be achieved by changing the austenitizing temperature. This change also influences the bainitic lath as well as retained austenite post austempering. This study focuses on investigating the mechanical strength, ductility and fracture toughness of nano-structured bainitic steels with different austenitizing temperature but similar austempering temperatures.