Since prevention methods of type-II diabetes and knowledge of prediabetes are lacking, the development of sensitive and accurate glucose sensors with an ultralow detection limit is imperative. In this work, the enzyme-free glucose sensor based on three-dimensional (3D) hierarchical Ni microflowers with a Ni(OH)2 coating layer has been demonstrated in a simple one-step chemical reaction at a low temperature of 80 °C. The as-synthesized materials were characterized by several analytical and spectroscopic techniques. In addition, the thin Ni(OH)2 layer formed at the surface of the Ni microflower was evidenced by Raman, HRTEM, and XPS, which is the key factor to achieve highly sensitive enzyme-free glucose sensors based on low-cost materials such as copper, nickel, and their oxide and hydroxide. Moreover, our modified electrode exhibits an outstanding detection limit as low as 2.4 nM with an ultrahigh sensitivity of 2392 μA mM-1 cm-2, which is attributed to not only the increased surface area due to the controlled formation of spikes but also the contribution of the Ni(OH)2 coating layer.