Melt spinning rapid solidification technique was employed to fabricate homogeneous Al-ln immiscible alloys and their final microstructures and morphologies were investigated. There existed a transition of columnar Al grain(-)equiaxed grain for the thicker ribbon, but only columnar Al grain for the thinner ribbon throughout the thickness. In the columnar grain field, most of the fine In particles was distributed within the cells, but a minority of bigger In particles or short rods was perpendicularly distributed at the grain boundaries. In the equiaxed grain field, the fine In particles were located in Al grains and coarser particles were situated at the boundaries. The average particle size increased with increasing distance from the chilled surface throughout the ribbon. At the same wheel speed (same cooling rate), the average particle size increased with raising In content. At the same composition condition, the average particle size decreased with increasing wheel speed and/or decreasing ejection temp Melt spinning rapid solidification technique was employed to fabricate homogeneous Al-ln immiscible alloys and their final microstructures and morphologies were investigated. There existed a transition of columnar Al grain (-) equiaxed grain for the thicker ribbon, but only columnar Al grain for the thinner In the columnar grain field, most of the fine In particles was distributed within the cells, but a minority of bigger In particles or short rods was perpendicularly distributed at the grain boundaries. In the equiaxed grain field, the fine In particles were located in the boundaries. The average particle size increased with increasing distance from the chilled surface throughout the ribbon. At the same wheel speed (same cooling rate), the average particle size increased with raising In content. At the same composition condition, the average particle size decreased with increasing wheel speed and / or decre asing ejection temp