Non-aqueous organic material-based redox flow batteries (NAORFBs) possess the advantage of using organic solvents to achieve high electrochemical potential. However, regardless of the great progress made in this regard in the past decade, further development has been restricted by the lack of stable electroactive organic materials and highly selective separators. Here, we present a NAORFB with all-PEGylated, metal-free, organic compounds as electroactive materials. PEGylated phenothiazine and PEGylated viologen are utilized as the catholyte and anolyte, respectively. Combined with a composite nanoporous aramid nanofiber separator, the all-PEGylated NAORFB presents outstanding cyclability, with a capacity retention of 99.90% per cycle and average coulombic efficiency of 99.7%. By contrast, NAORFBs using half-PEGylated and non-PEGylated electrolytes display inferior cyclability owing to the crossover of non-PEGylated materials. An extended investigation was also performed on the batteries using non-PEGylated or half-PEGylated materials for mechanistic elucidation. This work validates the PEGylation strategy in NAORFBs for enhanced overall performance with respect to solubility, cyclability, and alleviated crossover.