The effects of antimony (Sb) addition on the microstructure and mechanical properties of rapidly solidified eutectic Al-Si alloy were investigated. Al-12 wt.%Si-Xwt.%Sb (X = 0, 0.5 and 1.0) alloys were fabricated using a melt-spinner at rotating speeds of 20 mm. The as-melt-spun ribbons were characterized by a combination of scanning electron microscopy (SEM), X-ray diffraction (XRD) and depth-sensing indentation (DSI) methods. SEM observations showed that 0.5%Sb addition refined the microstructure whereas 1.0%Sb addition led to the formation of coarse Si particles. The wheel side of the ribbons exhibited a finer microstructure than those on the free or air sides exposed to the atmosphere. According to the XRD results, the diffraction patterns of melt-spun ribbons consisted solely of alpha-Al and Si phases, and a possible volume fraction of AlSb or an intermetallic phase in the alloy was not observed. DSI tests were performed on the ribbons under different loads ranging from 200 to 1200 mN at room temperature. The resulting indentation load-displacement (P-h) curves were analyzed using the work of indentation approach (WIA) to evaluate the ribbons' microhardness (H) and reduced modulus (Er). We found that the H and Er values of the ribbon decrease with increasing Sb content. This can be attributed to the over modification and changes in the microstructure of Al-12%Si alloy when a minimum of 1.0%Sb is present as a modifier. (C) 2010 Elsevier B.V. All rights reserved.