Al-Bi alloy has a low friction coefficient and high wear-resistant properties and is a good self-lubricating material for advanced bearings in automotive applications if the soft Bi-rich phase is dispersedly distributed in the comparatively harder Al-based matrix. However, Al-Bi alloy is a typical immiscible alloy. When cooling a homogeneous single phase liquid of Al-Bi alloy in the miscibility gap, it transforms into two liquids. The liquid-liquid phase transformation generally leads to the formation of a phase segregated microstructure. In the last decades, considerable efforts have been made to study the solidification behavior of Al-Bi alloy. It is demonstrated that the microstructure evolution during the liquid-liquid decomposition is a result of concurrent actions of the nucleation, growth, Ostwald ripening and motions of the Bi-rich droplets. The nucleation and the immigration of the Bi-rich droplets show a dominant influence on the solidification microstructure of Al-Bi alloy. Enhancing the nucleation rate and reducing the Marangoni migration velocity of the Bi-rich droplets promote the formation of a well dispersed microstructure. Considering that addition of surface active element to the alloy may result in a reduction in the liquid-liquid interface energy, and thus reduce the nucleation energy barrier and Marangoni migration velocity of the Bi-rich droplets, the possibility to control the solidification process and microstructure of Al-Bi alloys by adding micro-alloying element Sn was investigated. The experimental results show that microalloying element Sn can cause an effective refinement of the Bi-rich particles. The refining effect increases with the increase of Bi content up to 0.10%Sn (mass fraciton). A model was developed to calculate the microstructure formation. The numerical results demonstrate that Sn can act as an effective surface active element for Al-Bi alloys and promote the formation of a well dispersed microstructure.