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Aluminum (Al) toxicity is the main factor limiting plant growth and the yield of cereal crops in acidic soils. Al-induced oxidative stress could lead to the excessive accumulation of reactive oxygen species (ROS) and aldehydes in plants. Aldehyde dehydrogenase (<i>ALDH</i>) genes, which play an important role in detoxification of aldehydes when exposed to abiotic stress, have been identified in most species. However, little is known about the function of this gene family in the response to Al stress. Here, we identified an <i>ALDH</i> gene in maize, <i>ZmALDH</i>, involved in protection against Al-induced oxidative stress. Al stress up-regulated <i>ZmALDH</i> expression in both the roots and leaves. The expression of <i>ZmALDH</i> only responded to Al toxicity but not to other stresses including low pH and other metals. The heterologous overexpression of <i>ZmALDH</i> in <i>Arabidopsis</i> increased Al tolerance by promoting the ascorbate-glutathione cycle, increasing the transcript levels of antioxidant enzyme genes as well as the activities of their products, reducing MDA, and increasing free proline synthesis. The overexpression of <i>ZmALDH</i> also reduced Al accumulation in roots. Taken together, these findings suggest that <i>ZmALDH</i> participates in Al-induced oxidative stress and Al accumulation in roots, conferring Al tolerance in transgenic <i>Arabidopsis</i>.