This study aims to investigate the potential of nanoparticle retention of ultrafi ltration (UF) multichannel hollow fiber membrane. Filtration experiments of fl uorescent silica nanoparticles (NPs) (10 and 100 nm) and CdTe quantum dots (1.5 nm) suspensions were carried out under diff erent operating conditions to analyze the retention rate (RT), the fouling zone and the membrane productivity. Fouling mechanism occurring during the experiment has been correlated with the distribution profi les of NPs obtained during the membrane autopsy after fi ltration by Confocal Laser Scanning Microscopy (CLSM). Results show that large NPs are totally retained on the membrane surface. Medium NPs pass through the membrane at the beginning of the fi ltration and are gradually stopped in the membrane skin before forming a deposit on the membrane surface. The retention rate of small NPs also increases over time and an in-depth fouling of the membrane (skin + support) has been identifi ed. Mass balance and determination of NPs surface deposit thickness, in the case of a filtration cake, determined by CLSM and scanning electron microscopy (SEM) allowed the estimation of NPs amount trapped in the membrane structure (skin or support) and have been compared to the fouling resistance observed during the filtration run. The CLSM analysis of the membrane on its section presents, in that study, a signifi cant interest because of the high accuracy of the measures: 538.16 nm compared to the 5000 nm reported in a previous study.