Stable nanoparticle solution is the key parameter to obtain a uniform coating layer on the membrane surface without any aggregation for an efficient photocatalytic activity. In this study, a commercial titanium dioxide (TiO2, P25) was used to functionalize the nanofiltration (NF) membrane surface to be able to increase the water disinfection effects of the membrane. A polymer (Polyethyleneimine, PEI) bonding was used to be able to disperse TiO2 evenly in the solution by using newly modified hydrothermal method. Stability tests were conducted to test the stability of the nanomaterial in suspension. For surface coating, the NF membrane was incubated in contact with the uniform/stable nanoparticle solution. Contact angle measurements were conducted to evaluate the surface characteristic of the functionalized membrane and antibacterial tests were performed to evaluate the water disinfection effects of the functionalized membrane.