Additively manufactured AlSi10Mg alloys have received considerable attention due to the prospectives in light-weight structural applications. Hot isostatic pressing (HIP) is widely utilized to minimize internal pores and enhance mechanical properties in terms of fatigue strength and ductility. Whereas the influence and mechanisms of HIP on surface properties, which is of crucial importance for aerospace optical components, remain to be further clarified. In the present study, systematic surface and subsurface analysis were conducted to unveil the underlying mechanisms of HIP on the surface qualities of an additively manufactured AlSi10Mg alloy. Three-dimensional white-light interfering profilometer, high-resolution X-ray micro computed tomography, X-ray diffraction, scanning electron microscope and transmission electron microscope were exploited to characterize the surface and subsurface alterations induced by HIP. The results demonstrate that, although remarkable reduction in the amount and size of internal pores can be achieved, sharp increase in the surface defects and roughness occurred for the precisely machined surface of the HIP treated alloy. Surface and subsurface analysis reveal that the deterioration in surface properties results from the establishment of micron Si particles and the reduction in nanohardness induced by HIP treatment. © 2024 Elsevier B.V.