This study aimed to investigate the effects of pure oxygen aeration on extracellular polymeric substances (EPS) of activated sludge treating saline wastewater in a sequencing batch reactor (SBR). Activated sludge with pure oxygen aeration was more effective for TOC removal than that with air aeration when salinities were less than 3.0%. The soluble microbial products (SMP) concentrations with pure oxygen aeration were higher at low salinities (0.5%, 1.0%), while the opposite occurred at high salinities (2.0%, 3.0%, 4.0%). The EPS concentrations of the two aeration methods were similar when salinities were at 0.5% and 1.0%, while higher amount of total EPS would be produced in pure oxygen aeration reactor when the salinities were above 2.0% (p<0.05). The fluorescence peaks in both loosely bound EPS (LB-EPS) and tightly bound EPS (TB-EPS) of activated sludge with pure oxygen aeration at 3.0% salinity were attributed to tryptophan PN-like substances and humic acid-like substances. The sludge volume index (SVI) showed linear correlations with EPS (R-2 = 0.9057), PN (R-2 = 0.9741) and PS (R-2 = 0.8833) at 3.0% salinity, respectively. In pure oxygen aeration system, SVI was more sensitive with EPS and PN, which may worsen settling performance of the sludge. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.