Star-shaped block copolymers (SPs) have shown promise as antifouling coating materials on water purification membranes. The unique architectural design of these SPs, composed of covalently linked hydrophobic core and hydrophilic arms, offers the flexibility of tailoring the core and/or arm compositions to achieve properties on demand. Here, variable sizes of SPs with increasingly hydrophobic polystyrene cores (PSCs) and longer hydrophilic poly(ethylene glycol) (PEG) arms were synthesized to evaluate their coatability on polysulfone ultrafiltration (PSF UF) membranes and to study the effect of the hydrophilic PEG arm lengths on the antifouling properties of SP-coated membranes. The oleophobicity evaluated from underwater hexadecane contact angle (CA) measurements of SP-coated membranes increased by approximately 3 times, leading to almost 7 times improvement in permeation flux during oil emulsion filtration. No flux recovery was observed for the pristine PSF membrane, whereas 100% flux recovery ratio (FRR) was achieved for SP-coated membranes. The filtration of bovine serum albumin (BSA) protein solution exhibited an improvement in the permeation flux by 2.7-8.9 times for SP-coated membranes. The FRR was only 64% for the pristine PSF membrane, as opposed to nearly 100% FRR for all SP-coated membranes. The stability of the SP coating was tested by rigorous washing with Tween 80 surfactant and three-cycle oil emulsion filtrations. Surfactant washing only removed the loosely bound extra layers of SP coating, leaving the surface-bound and pore-entrapped stable SP coating with remarkable antifouling properties. Since SP3 with the largest hydrophobic PSC showed much better performance, the effect of increasing its PEG arm length on the antifouling properties was studied further, and the largest size SP3 with the longest PEG arm was the optimum antifouling coating. This study provides insights into the design of block copolymer nanoarchitecture to develop antifouling surfaces of interest ranging from water purification to biomedical applications.