The effects of cooling rate and Nd modification on the microstructure of hypoeutectic Al-11 Mg₂Si alloy were investigated. The results indicate that the microstructure of hypoeutectic Al-11 Mg₂Si alloy is composed of primary α-Al and（α-Al+Mg₂Si） phase. With the increase of the cooling rate of the mould, the eutectic temperature is decreased and the undercooling is increased, where the area fraction of primary α-Al phase is gradually decreased, and the Mg₂Si eutectic phase is converted from coarse lamellar to fine fibrous. Moreover, the secondary dendrite spacing of Mg₂Si phase is decreased and the microstructure is refined. After 0.4% Nd modification, with the increase of cooling rate, the addition of modifier leads to the partial melt undercooling of Mg₂Si eutectic during solidification, improving the nucleation rate. Mg₂Si is uniformly distributed in form of flocculent in eutectic of Al-11 Mg₂Si alloy