In this work, graphene oxide (GO) was combined with polyethersulfone (PES) to form mixed matrix membranes (MMMs) for ultrafiltration of aqueous solutions. Also, the effect of adding various pore formers (poly(vinylpyrrolidinone (PVP), reverse triblock Pluronic (P31R1), and poloxamine Tetronic (T904)) to the dope solution was investigated. The prepared MMMs were characterised using various techniques, including Fourier-transform infrared spectroscopy, scanning electron microscopy and atomic force microscopy. It was found that the incorporation of 0.5 wt% of GO increased the flux from 2 to 13 L m(-2) h(-1) (LMH) and the rejection of bovine serum albumin (BSA) from 89.2 to 97% compared to benchmark PES membranes. SEM analysis revealed the increased pore size and porosity of the GO modified membranes, which contributed to the increased flux. The addition of pore formers further increased the flux compared to pure PES and also displayed synergistic effects with GO. The combination of T904 with 0.3 wt% GO increased the water flux significantly from 2 to 245 LMH and increased the rejection of acridine orange (from 40.5 to 48.4%) and BSA (from 89.6 to 93.3%), respectively. Also, fouling properties of the membranes were investigated with the parameters: flux recovery ratio (FRR), total flux decline ratio (R-t), reversible flux decline ratio (R-r), and irreversible flux decline ratio (R-ir), and improved anti-fouling properties were obtained with the addition of GO. This work shows the promise of GO as a performance- enhancing additive in MMMs for wastewater treatment.