A full scale waste water reuse plant suffered from irreversible fouling of the reverse osmosis (RO) membranes. The major suspect of fouling is cationic organic polymers applied in the wastewater sludge treatment. Thus, the purpose of this research is to study the effect of six cationic polymers, applied in the plant, on RO membrane performance. The filtration and adsorption experiments with 4 mg C/L polymer solutions were performed in laboratory RO set ups for 5–7 days. Scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy were used to analyze polymers. Fouling prediction was calculated with Modified Fouling Index-ultrafiltration (MFI-UF) constant flux values. A flux decline of 30–50% was observed after filtration experiments. In adsorption experiments, the resistance increased from 6 to 35%. The MFI-UF results showed the rate of fouling was around 1 bar/month. The base-acid cleaning was able to reduce the resistance of the fouled membrane with irreversible fouling resistance, 6–7%. SEM images showed that the fouling layer after cleaning did not appear in the membrane. The FTIR spectra of the membrane after cleaning were similar to virgin membrane. However, several adsorption peaks on the membrane after cleaning were not restored to the initial state.