Abstract: The effects of the addition of Si on the microstructures and properties of SAl5356 aluminum alloy wire and its tensile properties of butt-welded joints with SAl5356 as the filler were investigated. Results showed that, when the content of Si ranged from 0 to 0.12%, the tensile strength of SAl5356 wire and its welded joint was improved slightly with the increase of Si content, while the plasticity was just the opposite. When the content of Si was higher than 0.12%, some coarse silicon rich phases were found in the microstructures of SAl5356 wire and its weld, and all properties, especially plasticity, dropped with the increase of Si content. In particular, when the Si content was above 0.2%, the coarse silicon rich phases were enriched at the grain boundaries, and forming fish-bone-shaped eutectic structure with α(Al) matrix, and their tensile properties dropped more obviously. The tensile strength of SAl5356 aluminum rod with Si content 0.25% was decreased 12% from its peak, while the elongation was decreased 45% from its peak. Therefore, to improve the performance of SAl5356 aluminum wire and its weld, Si content should not be more than 0.2%, and the optimum content of Si was less than 0.12%.