The influence of lanthanum (La) addition on the solidification structure of a casting Al-Cu alloy has been studied. It is found that the addition of 0.3 wt.% La has a significant grain refining effect on the alloy. Microstructure characterization reveals that a large number of globular grains have fine block-shaped Al-Ti-V-La particles in the centers. It is suggested that the dispersed Al20(Ti,V)2La particles precipitated in the aluminum melt have acted as heterogeneous nucleation sites for the a-Al grains during solidification. Moreover, during the growth of a-Al grains, La will be accumulated in the liquid of solidification front due to segregation. Another influence of La on the grain refinement is attributed to the restriction effect of La on the grain growth of a-Al grains during solidification. Keywords: Al-Cu alloy, grain refinement, rare earth, heterogeneous nucleation, Lanthanum.