Abstarct: Zinc oxide nanostructure was prepared by using zinc acetate (as precursor) and carboxylic derivative of activated carbon (as matrix). Activated carbon was modified by oxidation with nitric acid to get carboxylic derivative (AC–COOH), then zinc was loaded on the surface of modified activated carbon by an impregnation method. The ZnO nanostructure was characterized by BET, XRD and SEM. The prepared ZnO nanostructure consisted of ZnO nanoparticles with a size of 31-21nm and its surface area was 17/78 m2 g-1. The efficiency of the resulting catalyst was evaluated in the photocatalytic decomposition of aqueous solution of azo dye methyl orange (MO). Activity measurements performed under UV radiation showed good results for the photodegradation of MO. The efficiency of catalyst prepared with non-modifided activated carbon for the photodegradation of MO was also evaluated. The results confirmed that ZnO prepared by using carboxylic derivative of activated carbon as matrix have better photocatalytic activity than ZnO prepared by unmodified carbon active matrix.