This study investigates the effect of laser shock peening (LSP) on the microstructure and properties of GX4CrNi13–4 martensitic stainless steel. Three different conditions of surface preparation were examined in this study. First, a control group was left with a ground surface. The two remaining groups were treated with LSP. In one case, a single pass of LSP was applied and in the other case, a double pass of LSP was concerned. The samples were subsequently subjected to corrosion-fatigue testing in a water solution of 0.5 g/l NaCl, metallographic analysis, X-ray diffraction, and microhardness measurements. Experimental results of the corrosion-fatigue test showed that the LSP-treated samples exhibited fatigue cracking at higher force amplitude. Roughness mea-surements showed that the surface after LSP was rougher compared to the initial ground surface but with a lower proportion of grooves. Greater plastic surface deformation resulted in an increase in microhardness in the near- surface region, which was accompanied by an increase in the calculated density of geometrically necessary dislocations, a decrease in the proportion of retained austenite and coarsening of the martensite phase crystallite.