•ZnO nanoflowers were synthesized by a facile solution route with dextran assistance.•Dextran promoted the formation of ZnO nanoflowers.•ZnO nanoflowers showed high photocatalytic activity of methyl orange degradation.Flower-like zinc oxide nanostructure was successfully synthesized by a facile solution route with dextran ((C6H10O5)n) assistance. This ZnO nanoflower consists of several petals, and each petal is composed of many nanorods. If not using dextran in the preparation process, only larger fragments could be obtained. The effects of dextran on the conversion of zinc species and the formation of flower-like ZnO nanostructure were discussed and the possible growth mechanism was tentatively proposed based on the experimental results. Furthermore, this flower-like ZnO nanomaterial exhibits higher activity than ZnO fragments obtained without dextran on the photocatalytic degradation of methyl orange, which shows the potential application for wastewater treatment.