Abstract: To clarify the grain evolution behavior and aging response characteristics of 15-5PH stainless steels with different Ni contents during hot rolling, to reveal the effects of hot-rolling process parameters and alloy composition on the microstructural evolution and mechanical properties, and to provide a theoretical basis for the optimization of hot-rolling processing and compositional design of 15-5PH stainless steel plates. At a rolling speed of 0.4 m/s, the effects of two hot rolling temperatures （1 080 ℃ and 1 030 ℃） and four deformation levels （70%, 44.4%, 65%, and 28.5%） on grain evolution and aging properties of 15-5PH stainless steels with different nickel contents were systematically investigated. The results indicate that during the first hot rolling at 1 080 ℃, the plate microstructure exhibits a clear tendency toward inheritance and coarsening after heavy deformation of 70% and 65%, with no recrystallization occurring. When the once-rolled plate undergoes secondary rolling at 1 030 ℃, the prior deformation history plays a decisive role in grain evolution. Secondary rolling of the plate pre-deformed by 70% （with a second-pass deformation of 44.4% and a cumulative deformation of 83.3%） fails to refine the grains. In contrast, secondary rolling of the plate pre-deformed by 65% （with a second-pass deformation of 28.5% and a cumulative deformation of 75%） induces complete dynamic recrystallization, resulting in an equiaxed fine-grained structure, which represents the optimal hot rolling process. The hot rolling grain evolution trends are consistent across the three experimental steels, indicating that within the scope of this study, variations in nickel content under the same process have no significant impact on the grain evolution behavior. As the aging temperature increases, the strength of the three experimental steels decreases and the plasticity increases. The higher nickel content, the lower the strength. The primary reason is that nickel in the steel promotes the formation of reversed austenite, and the increase in austenite volume fraction reduces the strength of the steel. The research is not limited to the final deformation, but reveals its decisive role in grain evolution by analyzing the complete process path of multi-pass hot rolling. The findings are expected to provide direct experimental evidence for the independent optimization of composition design and hot rolling processes, offering important theoretical guidance for the precise engineering production of 15-5PH stainless steel plates.