With zinc acetate and sodium hydroxide used as raw materials, while polyethylene glycol employed as dispersant agent, ultrafine zinc oxide flowers were successfully synthesized by hydrothermal method. The influence of the concentration of PEG20000 on the morphologies of ZnO flowers was discussed. The as-synthesized ZnO flowers consisted of microrods with hexagonal morphologies. The crystal structure and ultraviolet absorbing performance of ZnO flowers were also characterized using XRD, UV-VIS absorption spectrum. The results indicate that ZnO flowers are hexagonal wurtzite structure with high purity. There is a strong excition absorption peak at 300 nm in UV-VIS absorption spectrum and blue shift existed obviously.