NiO-ZnO nanocomposite photocatalysts were synthesized by co-precipitation/co-gel formation techniques using potassium hydroxide (KOH), sodium carbonate (Na(2)CO(3)) and oxalic acid (H(2)C(2)O(4)) as precipitating agents. X-Ray diffraction (XRD) analysis was employed for the determination of crystallite size and phase purity, while BET surface areas were estimated by nitrogen physisorption analysis. The photocatalytic activities of the NiO-ZnO nanocomposites, evaluated using the photo-decolourization of two structurally different dyes, methyl orange and methylene blue, were correlated with the variation in the crystallite size of the constituents of the composites. All the three synthesized nanocomposites showed appreciable activity for the decolourization of dyes. NiO-ZnO nanocomposite derived by KOH exhibited maximum activity for the decolourization of both the dyes and the decolourization rate of methylene blue was found to be comparable with that of Degussa P-25 TiO(2). Finally, the activity of the most active NiO-ZnO composite with relatively large crystallite sizes was compared with the pure components and their physical mixture, synthesized by the identical synthetic route, in the same molar ratio as that of nanocomposite.