Aim To testify the inhibitory effects of transforming growth factor ( conjugated with cytotoxin saporin on proliferating vascular smooth muscle cells. Methods Conjugation of saporin to TGFα was accomplished after derivatization of saporin and TGFα with N succinimidyl 3 (2 pyridyldithio) proprionate and final purification of the conjugate was achieved within Eppendorf Centrifugal Filter Tubes. Biological assay of cytotoxicity was measured by MTS (a colorimetric method). The studies of influence of TGFα-Saporin on values of Thymidine incorporation into SMCs were measured by 3 H thymidine uptake and receptor competition studies of TGFα-Saporin are measured by adding excess TGFα in SMCs exposed for TGFα-Saporin. Results Biological assay of cytotoxicity assays testified TGFα-Saporin conjugate could inhibit specially proliferation of SMCs in culture. The absorbances measured by MTS of the group treated by TGFα-Saporin(10 7 mol/L)reduced to 60% comparedwith the control group(P=0.0003). However, the absorbances of the group treated by saporin (10 3 mol/L) only reduced to 40% of the control group. The values of thymidine of TGFα-Saporin group (10 9 mol/L) in comparison significantly decreased to 60.9% of the control group (P<0.05), suggesting that cellular DNA synthesis obviously decreased as TGFα-Saporin was added. Saporin did not affect cellular DNA synthesis at 10 3 mol/L. But excess TGFα(10 7 mol/L) added in SMCs exposed for TGFα-Saporin (10 9 mol/L) can completely blocked the inhibitory effects of TGFα-Saporin so that 3 H thymidine uptake in the group was similar compared with the blank control group. Conclusions TGFα-Saporin possesses the more effective cytotoxicit.