The present study deals with the austenite stability and M 2 C carbide decomposition in three secondary hardening ultra-high strength (SHUHS) steels with varying levels of Cr and Mo (2Cr-1Mo, 2Cr-3Mo and 5Cr-5Mo) investigated using Vicker's hardness, optical and electron microscopy. These steels were subjected to high temperature austenitizing treatments at 1000, 1050, 1100 and 1150 o C. It has been established that increasing both Cr and Mo to 5wt. % as well as increasing the austenitizing temperature in this class of SHUHS steels is stabilizing the austenite such that almost 100% austenite is produced upon oil quenching. Further, higher Cr and Mo is also found to influence the stability of metastable M 2 C carbide formed during processing of the steels. While the M 2 C carbide in 2Cr-3Mo steel remained untransformed, it was found to transform partially to M 6 C during austenitization of 5Cr-5Mo steel. Hardness measurements on these steels revealed that hardness is relatively insensitive to austenitizing temperature in 2Cr-1Mo steel, decreased in 2Cr-3Mo and decreased more drastically in 5Cr-5Mo steel with austenitizing temperature. This dependence has been correlated to the influence of composition on M s temperature and hence on retention of austenite as well as primary carbides. The experimental results were compared against theoretical calculations using ThermoCalc, which predict the presence of only M 6 C in both 2Cr-3Mo and 5Cr-5Mo steels. The apparent discrepancy between theoretical and experimental observations has been correlated to kinetic factors.