The objective of the present paper is to investigate if the presence and the nature of austenite in 9Ni steel, together with the modification of the matrix induced by heat treatment, change the low cycle fatigue response. The steel was therefore heat-treated so that either a quenched martensitic matrix or a mixture of tempered martensitic with bainitic matrix containing retained or reversed austenite would be obtained, respectively. The experiments showed that while higher stress levels were observed during low cycle fatigue, the quenched microstructure presented a lower fatigue performance under the same applied strain. According to the slip marks pattern, the tempered steel exhibited a higher degree of cyclic deformation accommodation. No obvious effect of austenite in terms of the TRIP effect has been evidenced and the matrix appeared to play a more important role in the fatigue performance. This investigation suggests another possible role of austenite.