Studies were conducted to investigate the membrane fouling and flux decline behavior that occurs while treating organic solutes contained in glycerinwater solutions (triglyceride, TG, and long chain fatty acid, FA). The analysis of the decline in flux over time while treating organic solutes was used to predict the fouling propensity. Two ultrafiltration membranes were tested: polyethersulphone (PES 25 kDa) and polyvinylidenfluoride (PVDF 30 kDa) membranes using glycerinwater solutions containing organic solutes (TG and FA). The influence of single TG and its combination with oleic acid (TGFA mixtures) as foulant models, pH of feed solutions (310), and membrane surface chemistry were investigated. Hermias model was applied, and the fitting of the experimental data to these models showed that the flux decline of PES membrane was dominated by pore blockage at the early stage and later by cake resistance during the entire filtration time. Conversely, for the PVDF membrane, the cake formation mechanism was acknowledged as the major contributor to the fouling mechanism for all the parameters tested. In consequence, the deposition mechanism was strongly influenced by the chemical nature of the membrane material itself, the nature of the foulants (TG and FA), and a combination of them as well as the chemistry of the feed solutions. Further, the model did not predict the performance over the complete duration of filtration, but two stages of filtration appeared to occur, involving pore blockage at the early stage followed by cake formation. It shows that fouling usually involves several mechanisms which occur simultaneously.