Very limited comparative research has been conducted on microstructure evolution induced by different peening methods. Herein, the 2024T351 aluminium alloy was subjected to conventional shot peening (CSP) and ultrasonic shot peening (USP) under the identical Almen height to investigate the differences in surface roughness, residual stress and microhardness. The results demonstrated that under the same Almen height, the CSP treatment resulted in a rougher surface with higher surface roughness and more surface defects, and higher surface and maximum compressive residual stress (CRS) than the USP treatment. In contrast, the CRS depth was relatively lower for the CSP treated samples. In addition, the USP treatment produced more significant microhardness and hardened layer than the CSP treatment.