Background:　Alzheimer＇s　disease　(AD)　is　a　common　cause　of　dementia　among　elderly　people.　Hyperphosphorylation　and　aggregation　of　tau　correlates　with　the　clinical　progression　of　AD;　therefore,　therapies　targeting　the　aggregation　of　tau　may　have　potential　applications　for　anti-AD　drug　development.　Several　inhibitors　of　tau　aggregation,　including　small　molecules　and　antibodies,　have　been　found　to　decrease　the　aggregation　of　tau　and　the　corresponding　pathology.　Objective:　To　screen　one　kind　of　single-chain　variable　fragment　(scFv)　antibody　which　could　inhibit　the　aggregation　of　tau　and　ameliorate　its　cytotoxicity.　Methods/Results:　Using　phosphorylated　tau　(pTau)　as　an　antigen,　we　obtained　a　scFv　antibody　via　the　screening　of　a　high-capacity　phage　antibody　library.　Biochemical　analysis　revealed　that　this　scFv　antibody　(scFv　T1)　had　a　strong　ability　to　inhibit　pTau　aggregation　both　in　dilute　solutions　and　under　conditions　of　macromolecular　crowding.　ScFv　T1　could　also　depolymerize　preformed　pTau　aggregates　in　vitro.　Furthermore,　scFv　T1　was　found　to　be　able　to　inhibit　the　cytotoxicity　of　extracellular　pTau　aggregates　and　ameliorate　tau-mediated　toxicity　when　coexpressed　with　a　hTauR406W　mutant　in　the　eye　of　transgenic　Drosophila　flies.　Conclusion:　This　scFv　T1　antibody　may　be　a　potential　new　therapeutic　agent　against　AD.　Our　methods　can　be　used　to　develop　novel　strategies　against　protein　aggregation　for　the　treatment　of　neurodegenerative　diseases.