Solidification of 0.1―1.0 mm diameter droplets of Fe-66.7 at.%Si alloy was achieved in a 3 m drop tube. The XRD, EDS, and SEM measurements reveal that all the droplets are composed of the primary phase α and the α+ε eutectic. With decreasing droplet diameter, the growth mode of the primary phase α changes from faceted to nonfaceted growth and the eutectic changes from needle-like to anomalous eutectic. In addition, the width of the primary phase α decreases with decreasing droplet size. The different cooling rates and undercooling levels corresponding to the samples with different sizes are responsible for the morphology changes. The cooling rates of the samples with different diameters during free fall were calculated and their effects on the microstructure formation were discussed. This kind of transition is also found inside the same sample, which is due to the larger cooling rate on the surface than at the center. The Solidification of 0.1-1.0 mm diameter droplets of Fe-66.7 at.% Si alloy was achieved in a 3 m drop tube. The XRD, EDS, and SEM measurements reveal that all the droplets are composed of the primary phase α and the α + ε with decreasing droplet diameter, the growth mode of the primary phase α changes from faceted to nonfaceted growth and the eutectic changes from needle-like to anomalous eutectic. In addition, the width of the primary phase α decreases with decreasing droplet size. The different cooling rates and undercooling levels corresponding to the mapping with different sizes are responsible for the morphology changes. The cooling of the samples with different diameters during free fall were calculated and their effects on the microstructure formation were discussed. This kind of transition is is also found inside the same sample, which is due to the larger cooling rate on the surface than at the center.