Zinc alginate (Alg-Zn) fibers were obtained by wet spinning of sodiumalginate (Alg-Na) into a coagulating bath containing an aqueous zinc chloride solution. ZnO nanostructures were prepared by thermal degradation of the as-obtained zinc alginate fibers at different temperatures in air. The compositions, morphologies, and microstructures of products were investigated by thermal gravimetry (TG), X-ray diffraction (XRD), electron energy-loss spectroscopy (EELS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). Annealing time and temperature influenced final structures and shapes of ZnO nanostructures. ZnO nanorods with diameters of about 120 nm were obtained at 800 and with a reaction time of more than 24 h in air. A ZnO growth mechanism was proposed by a careful investigation of ZnO nanostructures after different thermal treatment times.