The objective of the study was to compare the treatment efficiency obtained with the MIEX (R) DOC process and ultrafiltration as well as to investigate the effect of MIEX (R) DOC water pretreatment on the performance of ultrafiltration membranes. The influence of MIEX (R) resin dose and membrane cut-off on natural organic matter removal (NOM) efficiency was analyzed. Based on obtained results it might be stated that magnetic ion-exchange resin MIEX (R) is very effective in NOM separation from natural waters. For resin dose equal to 15 mL/L the reduction of abs 254 nm reached 90% for model solution and 80% for Odra river water. For UF membranes, their cut-off significantly influenced the NOM retention coefficient. The use of MIEX (R) DOC, process prior to ultrafiltration, increased permeate quality, especially for high MWCO membranes. Even very low MIEX (R) resin doses, significantly improved final water quality.