The redox state of tissues tends to become progressively more prooxidizing during the aging process. The hypothesis tested in this study was that enhancement of reductive capacity by overexpression of glucose-6-phosphate dehydrogenase (G6PD), a key enzyme for NADPH biosynthesis, could protect against oxidative stress and extend the life span of transgenic Drosophila melanogaster. Overexpression of G6PD was achieved by combining a UAS-G6PD responder transgene at one of four independent loci with either a broad expression (armadillo-GAL4, Tubulin-GAL4, C23-GAL4, and da-GAL4) or a neuronal driver (D42-GAL4 and Appl-GAL4). The mean life spans of G6PD overexpressor flies were extended, in comparison with driver and responder controls, as follows: armadillo-GAL4 (up to 38%), Tubulin-GAL4 (up to 29%), C23-GAL4 (up to 27%), da-GAL4 (up to 24%), D42-GAL4 (up to 18%), and Appl-GAL4 (up to 16%). The G6PD enzymatic activity was increased, as were the levels of NADPH, NADH, and the GSH/GSSG ratio. Resistance to experimental oxidative stress was enhanced. Furthermore, metabolic rates and fertility were essentially the same in G6PD overexpressors and control flies. Collectively, the results demonstrate that enhancement of the NADPH biosynthetic capability can extend the life span of a relatively long-lived strain of flies, which supports the oxidative stress hypothesis of aging.