The preparation, characterization and unique photoelectrochemical characteristics of a gold electrode chemically modified with suitably derivatized single-walled carbon nanotubes (SWCNTs) are described. The SWCNT-chemically modified gold electrode (CNT-CME) is assembled by linking acid-shortened SWCNTs with carboxylic groups at the nanotube ends to a gold surface previously modified with a cysteamine monolayer. A persistent photocurrent is observed when the modified electrode is illuminated with visible light in the presence of an electroactive species (ascorbic acid, AsA). The influence of physical variables (applied potential, light intensity) and of chemical parameters (AsA concentration, pH) on the generated photocurrents is evaluated. With an appropriate applied potential this device behaves as a photodiode.