In this study, the effect of the austempering times on the microstructures and mechanical properties of dual-matrix structure austempered ductile iron (DMS-ADI) was investigated. With this aim, unalloyed as-cast ductile iron tensile samples were austenitized at 810 degrees C for 30 min to intercritical austenitizing followed by austempering at 350 degrees C for various austempering times (45 min to 180 min). Experimental results showed that dual-matrix structures consisting of proeutectoid ferrite + ausferrite were obtained in austempered ductile iron from intercritical austenitizing temperatures. It was determined that as the austempering time increased, the ausferritic structure became considerably clear and its volume fraction was almost constant (45-47%) after 90 min of austempering time. The yield and tensile strength of the samples decreased and the total elongation and breaking energy increased with increasing austempering times, but after the 120-min austempering time, both the total elongation and breaking energy of the samples decreased. It was established that the austempering times had no significant effect on the morphology of ausferrite. The best mechanical properties were obtained between 70- and 130-minute austempering times that can be defined as the processing window. In addition, it was determined that the DMS-ADI had similar austempering kinetics with the ADI.