The presence of tin, which has a low solubility in an aluminium matrix, can affect the evolution of dendritegrowth with different contents. The evolution of the dendrite orientation during the unidirectional solidification of Al-Snalloys with different contents is investigated by optical metallography (OM) and electron back-scatter diffraction (EBSD).The macrostructure of the longitudinal section of the sample exhibits a single typical fan-like structure, regular columnargrains or both. The EBSD grain reconstruction maps and corresponding poles of different sections can demonstrate theactual dendrite growth directions. The results show that only columnar grains but no twinned dendrites are present in thedirectional solidification microstructures of low-tin-content Al-Sn alloys. When the Sn content reaches 4 wt.%, the preferredgrowth direction of some dendrites changes from <100> to <110>, and twinned dendrites with {111} as the twin boundarystarts to form. The macroscopic growth direction of the columnar crystals is parallel to the temperature gradient, whereasthe twinned dendrites, despite maintaining the <110> crystallographic orientation, have a macroscopic growth direction thatdeviates from the temperature gradient. The results indicate that the evolution of the dendrite orientation is related to thechange in the anisotropy of the interfacial energy. Under suitable solidification conditions, when the Sn content exceeds thecritical threshold, it can simultaneously cause changes in the growth pattern of dendrites and the preferred growth directionby altering the anisotropy of the interfacial energy.