The results of high-accuracy magnetic measurements on SUS 316LN austenitic stainless steel compressively deformed at room temperature (RT) are reported here. Even after the mild deformation of ∼25% true strain (ε t ), the ferromagnetic phase (α′-martensite) could be clearly observed which increased sharply on further deformation. The amount of α′ was very small (0.18 vol% at ε t ≈ 60%) when compared to the reported data for other grades of austenitic steels such as 304, 304L, 316, and 316L. The strain-induced α′-martensite is further studied by magnetic hysteresis loops. The coercivity (H C) and remanence (M r) were analyzed by subtracting the paramagnetic contribution of the bulk austenite structure. While H C was found to decrease with α′, M r remained the same (∼67 emu/g) when normalized to the volume fraction of α′. The decreasing H C with increasing α′ and/or ε t is presumed to be due to the domain wall pinning at the grain boundaries when the cluster size exceeds the domain wall width.