Abstract: The effects of austempering temperature (above/below martensite start (MS) temperature) and prior ausforming on the transformation kinetics, microstructure, and mechanical properties of a medium-carbon bainitic steel were investigated using a thermal simulation machine, scanning electron microscope, transmission electron microscope, electron backscattering diffraction, and tensile testing. The results show that for above-M_S austempering, prior ausforming accelerated the bainite transformation rate and refined the bainitic ferrite (BF) laths from 518 ± 155 to 454 ± 96 nm. However, an unexpectively increase in the fraction of blocky martensite and martensite/austenite blocks was observed due to the prior ausforming, which led to a reduction in the total elongation. In addition, without ausforming, when the austempering temperature decreased from above M_S (360 ℃) to below M_S (320 ℃), the bainite transformation rate was significantly enhanced and BF laths were further refined to 416 ± 77 nm. Nevertheless, excessive formation of athermal martensite (AM) was induced, resulting in a decreased bainite volume fraction and deteriorated elongation. For below-MS austempered and ausformed specimens, ausforming slightly decreased the bainitic transformation rate due to the sup-pression of AM formation caused by the lower MS temperature. Meanwhile, the volume fraction of bainite was increased and the finest BF laths (377 ± 51 nm in width) were obtained. Consequently, the below-M_S austempered specimens with ausforming exhibited the highest product of strength and elongation of approximately 26.12 GPa %.