Objective To establish a method using stirring ultrafiltration for isolating exosome from the culture supernatant of bone marrow mesenchymal stem cells(BMSCs). Methods The culture supernatant of BMSCs was collected and centrifuged at low speed to remove residual cells,and then the cell debris was removed by 0.22 μm filter. Then the clarified supernatant was purified by stirring ultrafiltration to obtain exosome. Transmission electron microscope was used to identify the morphology of exosome, Western blotting analysis was used to examine CD63, CD9 protein expression, and CCK-8 kit was employed to detect the effect of exosome on proliferation of human umbilical vein endothelial cells(HUVECs). Results Stirring ultrafiltration successfully isolated exosome from BMSCs culture supernatant; morphology of the isolated exosome was round or elliptic, with the diameter being about 100 nm. Results of Western blotting analysis showed positive expression of CD63, CD9 proteins. The exosome promoted proliferation of HUVECs in a dose-dependent manner. Conclusion Stirring ultrafiltration technique is a simple and efficient method for exosome isolation.