Hypoeutectic Al-Si alloys are extensively used in the welding industry owing to their excellent cast-ability, low coefficient of thermal expansion, and good weldability. Unfortunately, Al-Si alloys solidify under conventional cooling conditions, forming coarse dendritic α-Al grains with an eutectic structure and a flake-like morphology that has poor mechanical properties. Chemical inoculations are often used to control the size of α-Al grains and the morphology of the eutectic Si particles. The grain refiner Al-Ti-B master alloy and eutectic Si modifier Sr are commonly used in industry. In recent years, great attention has been paid to controlling the microstructure and mechanical properties of hypoeutectic Al-Si alloys through the use of the cost-effective rare earth element La. Previous studies have mainly focused on the effects of La addition on the microstructural evolution and improvements of the mechanical properties. However, to date there have been no studies on the effects of combined addition of La, Al-Ti-B master alloy and Sr on the microstructure and mechanical properties of Al-Si alloys. In this work, solidification experiments were performed to investigate the effects of the micro-alloying element La, Al-Ti-B master alloy, and Sr on the solidification microstructure and mechanical properties of hypoeutectic Al-Si alloys. These results show that synergistic effects are achieved by combinations of La, Al-Ti-B master alloy, and Sr. An addition of 0.06%La was sufficient for effective α-Al grain refinement, eutectic Si particle modification, and improved the ductility of the alloys. Excess La addition formed a coarse LaAlSi intermetallic compound, which deteriorated the ductility of the alloy. The micro-alloying element La refined the α-Al grains by acting as a surfactant that decreased the wetting angle between the TiB₂ nucleation substrate and the α-Al nucleus. It modified the eutectic Si particles by promoting the formation of the multiple Si twins and changing the growth behaviors of the Si particles.