The effect of a modified layer caused by pre-deforming on the low temperature plasma nitriding of AISI 304 austenitic stainless steel was investigated. The aim of using the deformed layer is to produce a thicker nitrided layer and to decrease the nitriding temperature due to the much faster diffusion of nitrogen. The pre-deformed sample was prepared by the rolling in 0, 1, 2, 3, and 4% ratios. Plasma nitriding was carried out at 673 and 723 K for 18 ks under 600 Pa pressures in presence of N2/H2 in 50:50 ratio. The microhardness, thickness and phase composition of nitrided layers formed on the surface of pre-deformed and non-deformed samples were investigated using Vickers microhardness tester, optical microscope and X-ray diffraction techniques, respectively. After nitriding, maximum hardness ~1150 HV was achieved on the pre-deformed sample. XRD pattern showed that most dominant phase of the nitrided layer consisted of the expanded austenite (S phase). In addition, the pre-deforming by rolling had a significant influence on the hardness and thickness of the S phase. That is, the hardness and thickness of the S phase were increased by applying the pre-deformation.