50 mL aqueous solutions of Polyethylene oxide (PEO) at 2 g/L were degraded at different frequencies in the range from 19 kHz to 1 MHz with 3 types of apparatus: horn, direct and indirect apparatus. Irradiation experiments were carried out at 20 ℃ and 5 W of dissipated power. Irradiated samples were then evaluated by Ubbelohde at 25 ℃. To suppress the chemical effects, t-BuOH was dissolved at 100 mM into the solution. PEO degraded rapidly at the first five minutes of irradiation then slowing down, approach to a limiting molecular weight, which depends on the irradiated frequency. Polymer degradation is influenced by physical effects mainly in the range from 20 kHz to 1 MHz. That calculated apparent degradation rate constant from data analysis is influenced by frequency is clearly understood. The higher frequency is, the lower physical