Enhancing permeation in microfiltration (MF) hollow fiber membrane process was studied under ultrasound (US) by means of reflection technique. The US effect on the enhanced membrane process depended on the position of membrane module with or without a semi-cylindrical shaped reflection plate placed behind the membrane module. Evidence was presented that the membrane process influenced the detected sonic pressure distribution in the US bath. The correlation of sound pressure intensity and luminol fluorescence intensity suggested that violent collapse of cavity bubbles supported the enhanced membrane permeability of MF module in the US bath.