Abstract: Ultrasonic techniques for measuring void content were discussed and the composites used for the whole fuselage composite aircraft developed independently in China were chosen as experimental specimens, including 10 unidirectional carbon fiber laminates and 10 textile glass fiber sheets. The ultrasonic RF signals were processed using Hilbert transform and spectral-filter and then used to calculate the acoustic attenuation. The relationship between attenuation coefficient and porosity was calibrated by sampling experiment based on metalloscopy. The calibrated relational expression was then used to estimate the porosity of the rest specimens. The experimental data showed that the ultrasound testing results were in agreement with the metallographic detection.