Hypersaline　organic　wastewater　is　characterized　as　being　nitrogen-deficient,　and　is　easily　prone　to　sludge　bulking.　In　this　study,　the　stability　of　halophilic　aerobic　granular　sludge　(HAGS)　for　the　treatment　of　hypersaline　organic　wastewater　is　explored.　Along　with　the　decrease　of　influent　ammonium,　the　bacterial　population　substantially　reduced,　whereas　the　fungal　population　continuously　increased　in　HAGS.　Saccharomycetales　in　fungi　become　the　dominant　sequence　(99.78%)　in　HAGS　bulking.　Additionally,　Halanaerobium　(77.47%)　remained　prevalent　in　HAGS　despite　bacterial　washout.　Halanaerobium,　a　nitrogen-fixing　genus　of　bacteria,　provided　nitrogen　for　ammonium-assimilating　fungi.　Saccharomycetales　encapsulating　HAGS　reduced　the　transfer　efficiency　of　dissolved　oxygen,　thereby　creating　favorable　growth　conditions　for　Halanaerobium.　This　paper　for　the　first　time　highlights　the　mutualistic　symbiosis　of　fungi　and　bacteria　in　HAGS　treating　the　hypersaline　organic　wastewater.　The　study　lays　the　foundation　for　the　control　and　recovery　of　HAGS　bulking.　©　2023