The main aim of this experiment is to determine the mechanical and microstructural of using Nano powder of Al2O3 besides stir welding of Al2024-T6 in multi-pass welding. Nanoparticles welded nine specimens and one particle-free in 1400 rpm rotational speed and 16 mm/min traveling speed. A combination of volume percentage of powder (3%, 5%, and 7%) and three different multi continuous passes (1, 2, and 4) is applied for Nano-rich specimens. The microstructure of joint, micro hardness and ultimate tensile strength (UTS) of the welded joint has been studied. It was observed that by increasing the particle volume from 3% to 7% average grain size increased extremely to 37% and UTS to 10%, and in the staid situation of welding passes, average micro hardness has 10% increase in shoulder affected zone. The result showed that the specimen with 7% of Nanoparticles in two passes has the highest mechanical and metallurgical properties and has a significant decrease (55%) in average grain size compared with a particle-free specimen. Meanwhile, UTS and average micro hardness of the same specimen was about 11% and 48% more than particle free.