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The objective of the present study was to examine the influence of laser peening without protective coating (LPwC) process on surface mechanical properties of precipitation hardened stainless steel 17-4 PH. Pulse densities, 2500 and 6250 pulses cm −2 , using a constant laser power density of 5.97 GW cm −2 were chosen and their effect on residual stresses, micro-structure, micro-hardness, surface roughness and topography were investigated. Higher pulse density induced large compressive residual stresses and influenced up to depth of 600 μm. It was confirmed from resulted larger lattice strain in LPwC processed 17-4 PH steel with higher pulse density. No phase transformation and microstructural change were observed, which represented pure mechanical effect of LPwC. Hardness was increased with depth of hardened layer up to 600 μm for higher pulse density. However, the surface roughness was increased by the process, and resulted in more pronounced peening pattern. Surface topography revealed columnar structure after LPwC process. [ABSTRACT FROM AUTHOR]