An ultrasonic time-domain reflectometry (UTDR) technique was used for the non-invasive, in situ visualization of particle deposition and its removal during crossflow microfiltration with a nylon membrane. The study was carried out with 0.5 g/l kaolin (average particle size 2 gm). Ultrasonic response signals were obtained upon particle deposition and subsequent cake layer formation on the membrane surface. A cake layer echo appeared in the time domain. The UTDR technique was also used to quantify the thickness of a fouling layer on the membrane surface. Moreover, UTDR was applied to monitor membrane cleaning and evaluate the effectiveness of various cleaning methods. Flux measurements and SEM analyses corroborated the UTDR results. Overall, the results confirmed the effectiveness of the UTDR technique for visualizing particle deposition on and removal from membrane surfaces.