Monodehydroascorbate reductase (MDHAR) is a key enzyme of the ascorbate-glutathione cycle that maintains reduced pools of ascorbic acid (AsA) and serves as an important antioxidative enzyme. cDNA encoding MDHAR was isolated from acerola (Malpighia glabra), a plant that accumulates very large amount of AsA. MDHAR transcript and enzyme activity were significantly up-regulated in acerola leaves under salt stress conditions, indicating that expression of MDHAR gene is transcriptionally regulated under salt stress. Acerola MDHAR cDNA was then introduced into tobacco plants using an Agrobacterium-mediated gene delivery system. Transgenic tobacco plants accumulated higher amount of AsA and showed higher MDHAR activity than the untransformed control plants. Lipid peroxidation and chlorophyll degradation were restrained in the transgenic plants under salt stress conditions compared to untransformed control plants. These results indicate that overexpressing of acerola MDHAR provided higher tolerance to salt stress.