ZnO microspheres were hydrothermally synthesized using triblock copolymer Pluronic F127 as a crystal growth modifier. The ZnO microspheres were composed of nanorods assemblies. The ZnO nanorods with a diameter of less than 100 nm were radially grown from the center in all directions. A possible growth mechanism is that ZnO seed species were stabilized in hydrophilic chains of Pluronic F127 micelles and that ZnO nanorods radially grew in the c direction from a center due to the effect of steric hindrance.