The bottleneck of skim milk ultrafiltration (UF) is the fouling phenomenon that affects the process performance thus limits the productivity. Several strategies have been chosen to control fouling. Some proposed to increase the shear rate close to the membrane [3], others suggested different procedures such as backpulsing[4], pulsating or reversed feed flows[5]. The ultrasonic-assisted filtration processes have been also proposed to enhance the cleaning process or the permeate flux. Several successful examples can already be found in literature [6-7]. Our recent work has shown a great interest to apply in-situ ultrasound (US) in colloidal suspensions filtration: with a designed ‘Cross-Flow US-coupled Filtration Cell’ at low US power (2 W.cm-2), a significant increase of permeate flux was observed without damaging the membrane structure [8]. Using the designed ‘SAXS Cross-Flow US-coupled Filtration Cell’, this study is devoted to enhance skim milk ultrafiltration by applying in-situ ultrasonication and to characterize effects of ultrasound at multi-scales: the macroscopic results, presented by the permeate flux, have been combined with simultaneous detections at nanometer length scale, revealed by in-situ SAXS measurements of synchrotron radiation [9]. Skim milk suspensions were prepared from ‘low heat’ Bovine Skim Milk Powder at C0=27 g.L-1 in casein micelle content. Figure.1a displays the evolution of permeate flux Jv, inlet/outlet pressures of filtration cell and cross-flow rate Qv over time. The filtration run is divided into 4 steps according to different operating conditions