This paper considers the output impedance of class-E amplifiers. Based on the load-pull principle, a circuit simulation and experiment is conducted. Sweeping the load resistance values, the RF output voltage and current amplitudes are plotted on the V -I plane. From the slope of the plotted device lines, the output impedance can be read. The output impedance shows 5.41 Ω in the simulation using an ideal switch. Replacing the ideal switch with a GaN FET, it becomes 5.32 Ω. To verify this result, we design and prototype a 100 W class-E amplifier at 6.78 MHz. The measured output impedance shows 5.14 Ω. The aforementioned three results are all in good agreement with the theoretical predictions, i.e. 0.405 times the nominal load resistance. In conclusion, the class-E amplifier has its output impedance of not 0 Ω, nor ∞ Ω, but of a finite specific value. This work puts an end to the controversy over the class-E amplifier’s output impedance. This work should be highly recommended to receive the IEICE technical paper award.