Novel three-dimensional (3D) flower-like Fe₃O₄ microspheres were synthesized by a facile precursor-templated conversion method. The precursor was prepared by an ultrasound-assisted hydrothermal method without the help of any surfactant. The possible formation mechanism of the precursor was proposed, and it was found that the synthetic parameters for the precursor such as the time of ultrasonic pretreatment and NH₄Ac concentration are crucial for the formation of the flower-like hierarchical precursor structure. The flower-like Fe₃O₄ microspheres obtained by calcining the precursor in N₂ exhibit superparamagnetic behaviour and show relative high saturation magnetization at room temperature. Furthermore, the as-obtained product, with high BET surface area, has been used as an absorbent in wastewater treatment and exhibit a strong capability to remove organic pollutants.