This study investigates the biofilm formation resistance of the multi-walled carbon nanotube (MWCNT) blended polyethersulfone (PES) membranes. The antimicrobial properties and biofilm formation resistance of these composite membranes were explored using Escherichia coli (E. coli) and Pseudomonas aeruginosa (P. aeruginosa) as model organisms. The results show that the dispersion of the MWCNTs in the membrane structure matters in determining the biofilm formation resistance of the composite membranes. Here, no colonies were observed on the composite membranes with 0.5 wt % of MWCNT content (C/P-0.5%) when the E. coli cells were deposited onto the membrane surface. Furthermore, when the membranes were incubated in P. aeruginosa suspensions, the C/P-0.5% membrane showed almost 87 % less biofilm formation at 24 h, with the biofilm formation resistance increasing to 92 % at 4 d, compared to the neat PES membrane. Finally, there was no MWCNT release during the water filtration of the composite membranes.