Zinc oxide (ZnO) particles with sword-like morphology were sonochemically synthesized from Zn(NO3)2−C6H12N4 aqueous solutions at 90°C. After the crystal growth, the ultrasonic irradiation facilitates the erosion process at the ends of hexagonal ZnO rods resulting in a sword-like morphology and reduces the overall crystal size. Increasing the ratio of C6H12N4 to Zn(NO3)2 from 1:2 to 5:1 increases the density of sword-like ZnO clusters. An extra absorption peak in the ultraviolet (UV) regime is observed in commercial polyurethane loaded with the surface modified ZnO. The dispersion of 15 wt% ZnO gives rise to a stronger UV absorption than that by 5 wt% ZnO.