Objective To explore the effective autologous bone marrow stem cell dosage for treatment of severe lower limb ischemia. Methods From December 2003 to December 2004, 22 cases of bilateral lower limb ischemia were treated with autologous bone morrow cell transplantation. All the patients were randomly divided into two groups according to ischemia degree. In group A(severe ischemia side), the amount of transplanted autologous bone marrow cells was more than 1×108, and ingroup B(mild ischemia side), the amount was less than 1×105. A series of subjective indexes, such as improvement of pain, cold sensation and numbness, and objective indexes, such as increase of ankle/brachial index (ABI) and transcutaneous oxygen pressure (TcPO2), angiography, amputation rate, and improvement of foot wound healing were used to evaluate the effect of autologous bone marrow stem cells implantation. Results The rates of pain relief were 90.0% in group A and 16.7% in group B (Plt;0.01); the rates of cold sensation relief were 90.5% in group A and 5.3% in group B（Plt;0.01）;the improvement of numbness was 62.5% in group A and 9.1% in group B（Plt;0.01）. Increase of ABI was 31.8% and 0 in groups A and B respectively（Plt;0.01） at 4 weeks after implantation. Increase of TcPO2was 94.4% and 11.1% in groups A and B respectively（Plt;0.01） at 4 weeks after implantation. Twelve cases of angiography showed rich new collateral vessels in 100% of the limbs in group A while no remarkable new collateral vessel in group B. The amputation rates were 4.5% in group A and 27.3% in group B（Plt;0.05） at 4 weeks after implantation. The rate of improvement of foot wound healing was 75% in group A and there was no changein wound healing in group B after 4 weeks of implantation. Conclusion The effectiveness of autologous bone marrow stem cell implantation depends on the number of implanted stem cells. Effectiveness is expected in most patients if the implanted stem cell is more than 1×108, whereas there would be little effect if the cell number is less than 1×105.