The　granule　instability　has　been　frequently　reported　during　the　operation　of　high　loading　rates.　While,　there　no　re-search　was　performed　on　the　recently　developed　anoxic　partial-denitrification　(PD)　granules,　a　novel　pathway　in　pro-ducing　nitrite　from　nitrate　for　anammox　process.　Herein,　this　work,　for　the　first　time,　investigated　the　influence　of　nitrate　loading　rates　on　the　instability　of　PD　granules　and　identified　the　key　causes.　Two　lab-scale　sequencing　batch　reactors　(SBRs)　were　operated　with　nitrate　loading　rates　(NLR)　increased　from　0.48　to　3.84　kg　N/m3/d　(R1,　8　cy-cles/d),　and　0.96　to　7.68　kg　N/m3/d　(R2,　16　cycles/d)　by　gradually　elevating　the　influent　nitrate　concentration.　Re-sults　showed　that　nitrite　production　rates　increased　with　the　NLRs,　with　a　maximal　value　of　5.26　kg　N/m3/d　obtained.　However,　the　compact　regular　PD　granules　were　not　stable　and　broke　down　when　NLR　was　above　3.84　kg　N/m3/d,　which　resulted　in　serious　sludge　washing　out　from　SBR.　The　high　NLRs　led　to　the　extracellular　polymeric　sub-stances　(EPS)　transformation　in　terms　of　its　composition　and　structure,　which　the　protein　content　in　the　EPS　and　the　tightly　bound　EPS　(T-EPS)　fraction　was　significantly　decreased,　this　was　supposed　to　be　the　major　reason　causing　the　breakdown　of　PD　granules.　Besides,　it　was　found　the　PD　granule　in　R2　was　more　deteriorated　than　that　in　R1　under　the　same　high　NLR,　suggesting　the　short　starvation　(idle)　times　in　SBR　cycle　was　likely　another　reason　impairing　the　stability　of　PD　granules.　Overall,　this　research　provides　useful　information　in　development　of　granule-based　PD　sys-tems　and　sheds　light　on　achieving　high-rate　nitrite　production　in　SBR　with　great　stability.