Zinc oxide nanoparticles doped with 0.2–1.5 mol% of Fe, Ni or Co and co-doped with 1 mol% of Ag were prepared by co-precipitation method and their photocatalytic activity in degradation of MB (methylene blue) water solution under ultraviolet irradiation was determined. X-ray diffraction analysis of the samples containing up to 0.5 mol% of iron group metals showed only ZnO and Ag phases. Crystallite size of doped ZnO nanoparticles was in the range of 27–31.6 nm depending on the sample composition and additional calcination at 400 oC. The photocatalytic activity of ZnO doped with iron group metals depended on the content of metals. The highest activity was observed for ZnO doped with 0.2 mol% of nickel. The co-doped with silver samples showed enhanced photocatalytic activity and higher reaction rate constant.