The particle morphology and composition of nanometer-scale Al3(Zr1-xTix) precipitates formed after aging at 450 °C for 1 h in Al-0.3mol%Zr-0.5mol%Ti alloy were investigated using high resolution electron microscopy (HREM) and three dimensional atom probe tomography (3D-APT). The alloy exhibits an inhomogeneous distribution of solute atoms after casting. After aging, Al3(Zr1-xTix) precipitates with a metastable L12 structure formed within solute-enriched dendrites. The Al3(Zr1-xTix) precipitate particles were spherical with diameters between 3 and 5 nm. The Al3(Zr1-xTix) precipitates were found to be coherent with matrix using HREM. Interfacial segregation of Ti at the matrix/precipitates was also observed in the composite Al3(Zr1-xTix) precipitates. The Zr:Ti atomic ratio in the Al3(Zr1-xTix) precipitates measured by 3D-APT was approximately 7 (x=0.125).