Abstract： Background Recently, arsenic trioxide (As2O3) was considered as a novel anti-tumor agent. However, it showed severe toxicity effect on normal tissue at the same time. To improve its therapeutic efficacy and decrease its toxicity,we prepared arsenic trioxide-loaded albuminutes immuno-nanospheres [As2O3-(HAS-NS)-BDI-1] targeted with nonoclonal antibody (McAb) BDI-1 and tested its specific killing effect against bladder cancer cell. Methods As2O3-HAS-NS was prepared by chemical cross-linking method. Monoclonal antibody BDI-1 was purified with ammonium sulphate saltingout and chromatography. Albuminutes microspheres were conjugated with McAb by SPDP cross-linking method.Concentration of As in As2O3- (HAS-NS)-BDI-1 and As2O3-HAS-NS was measured by atomic fluometry method. As2O3- (HAS-NS)-BDI-1 and its activity were detected by SDS-PAGE reduction electrophoresis, indirect immunofluorescence test, light microscope and scanning electron microscope observation. Acridine orange staining and tritiated thymidine (3H-TdR) incorporation tests were used to indicate specific killing activity of As2O3-(HAS-NS)-BDI-1 in vitro. Results In As2O3- (HAS-NS)-BDI-1 groups, we saw two protein bands in SDS-PAGE reduction electrophoresis.Albuminutes immuno-nanospheres were rounded with clear green fluorescence by immunofluorescence test. Under microscope, we observed that BIU-87 cells were covered with the As2O3- (HAS-NS)-BDI-1 and that As2O3- (HAS-NS)-BDI-1 moved with the BIU-87 cells. The albuminutes immuno-nanospheres were tightly junctioned with the BIU-87 cells.Specific killing activity of As2O3-(HAS-NS)-BDI-1 on bladder tumor cells was observed by acridine orange staining and 3H-TdR incorporation assays. Conclusions As2O3- (HAS-NS)-BDI-1 might bind specifically against BIU-87 cells, thus leading to high activity of killing bladder tumor cells.