In the application of ultrafiltration (UF) for removal of natural organic matter (NOM) from water, membrane fouling has always been considered a big issue. The influence of UV/TiO2 photocatalysis as pretreatment to mitigate cross-flow ceramic UF membrane fouling caused by humic acid (HA) and the involved mechanisms of fouling development were investigated. The characterization of dissolved organic carbon (DOC), specific ultraviolet absorbance (SUVA), excitation-emission matrix (EEM), molecular weight (MW), hydrophilicity, fouling resistance, scanning electron microscopy (SEM) and model fitting using Hermia blocking models were performed. The dominant membrane fouling patterns can be predicated by the initial intermediate pore blocking, transition fouling and the final stage of limited cake growth. With extended UV/TiO2 pretreatment time, a significant reduction of cake filtration coefficients and a slight decrease in pore blocking coefficients were observed. Longer UV/TiO2 pretreatment achieved the remarkable effect of reversible fouling elimination as a result of reaching the final stage of limited cake growth earlier and aggregation forming a porous cake layer by TiO2 particles mixed with more hydrophilic (HPI) and high MW ( > 50 kDa) humic-like substances. However, photocatalytic pretreatment exhibited a slight effect on the mitigation of irreversible fouling that was mainly dominated by HPI fractions, especially tryptophan-like protein (5-50 kDa) organics attaching to and/or blocking the membrane pores.