Abstract: Objective To observe the effect of magnetic nanoparticle containing arsenolite and polylactic acid in treatment of osteogenic sarcoma(OS)cell line UMR-106.Methods The magnetic nanoparticle containing arsenolite and polylactic acid were prepared,and transmission electron microscope(TEM)and fluorophotometer techniques were used to characterize its morphous and carrying dosage,and the heat effect on magnetic nanoparticle was studied under altering magnetic field in vitro.Then,the UMR-106 cells were cultivated,and MTT assay was performed to examine the effect of magnetic nanoparticle containing arsenolite and polylactic acid on the proliferation of UMR-106 cells.By FCM,the Percentage of apoptotic cells was detected.Results The prepared magnetic nanoparticle containing arsenolite and polylactic acid were well-distributed with an diameter between 60~70nm;As₂O₃ content is 10.3%.They had very distinct heat effect in a altering magnetic field and could rise to a steady temperature for tumor hyperthemia(41℃~46℃).Magnetic nanoparticle containing arsenolite and polylactic acid could significantly inhibit the proliferation and promote the apoptosis which were more distinct than the As₂O₃ solution and the Fe₃O₄ nanoparticle magnetic fluid.Conclusion Magnetic nanoparticle containing arsenolite and polylactic acid have both the cytoxicity,and the heating effects resulted from the radiofrequency-induced hyperthemia.This treatment has showed better effect on cell experiments than either using As₂O₃ or hyperthemia alone,and may provide a new way in clinical treatment for OS.