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Potassium (K⁺) is one of the most important macronutrients for plant growth and development. It is generally accepted that the KUP/HAK/KT transporters play essential roles in K⁺ uptake at low concentrations. However, their physiological functions in bananas remain unknown. Here, we cloned MaHAK5 and analyzed its functions in banana (<i>Musa acuminata</i>). Gene expression analysis showed that MaHAK5 was upregulated in the roots and leaves in the early stage of low K⁺ (LK) stress. MaHAK5 was localized in the cytomembrane. The expression of MaHAK5 improved the growth of the low K⁺-sensitive yeast mutant R5421 at different K⁺ supply levels. Overexpression of <i>MaHAK5</i> in <i>Arabidopsis thaliana</i> significantly enhanced the ability for K⁺ uptake and increased the chlorophyll content under LK stress. These results indicate that <i>MaHAK5</i> plays a crucial role in maintaining K⁺ uptake in bananas.