<p>In this study, Janus graphene oxide (JGO) nanosheets with different modification degrees using dodecylamine (DDA) as a hydrophobic agent were fabricated via a masking method, and their effects on flat polysulfone ultrafiltration membrane performance were evaluated. FE-SEM, FT-IR, CHN, and RAMAN analyses were used to characterize the nanosheets. Then, mixed matrix nanocomposite membranes with the same loadings of nanosheets were produced by the phase inversion method and characterized by FE-SEM, AFM, EDX, and contact angle analyses. The effects of the modification degree of JGO nanosheets on the surface properties, porosity, morphology, water uptake, pure water flux, fouling resistance, and rejection of the membranes were evaluated. The EDX analysis revealed that increasing the modification degree of JGO nanosheets with DDA reduced their migration toward the membrane surface while improving their orientation on the membrane surface. The results showed that increasing the modification degree of JGO nanosheets with DDA decreased porosity and water uptake in the membrane matrix. Furthermore, these modifications reduced the roughness and slightly improved the hydrophilicity of the membrane surface. These changes resulted in a decrease in the pure water flux from 224 L.m⁻².h⁻¹ in M_JGO-1 to 144 L.m⁻².h⁻¹ in M_JGO-3 and an increase in fouling resistance (increasing flux recovery ratio from 54 to 70% and decreasing total fouling ratio from 63 to 40%) of the membranes. Overall, this study revealed that the modification degree of JGO nanosheets can be adjusted to optimize the trade-off between flux and fouling resistance in ultrafiltration membranes.</p> Graphical abstract <p></p>