In this study, the hardenability of AISI 1050 steel has been investigated in different cooling media using Jominy test. The temperature values were recorded using the thermocouples that were placed on sample. The relations between the cooling media and the cooling curves, heat flux, hardenability and heat convection coefficient were shown in graphics. The correlation between thermal properties and hardenability was established. When Jominy water pressure decreased, hardenability decreased in Jominy bar. But hardenability of steel quenched by air-water mixture cooling media was observed that increasing surprisingly. As a result of air-water mixture quenching, heat transfer accelerated and the hardenability increased in the Jominy bar. (C) 2010 Elsevier Ltd. All rights reserved.