Objective To compare the hemodynamic effects of continuous spinal anesthesia（CSA）and small does single injection spinal anesthesia（SA） in 75 years or older patients. Methods In a prospective study, 40 American Society of Anesthesiologists Ⅱ-Ⅲ patients（aged 75 yr or older）, undergoing elective lower extremity surgery were randomLy assigned to either group CSA or group SA（n=20）. Group CSA received a starting dose of 5mg of 5% hyperbaric ropicaine, followed after 15 min by reinjecion of 2.5 mg every 5 min until a T12 level sensory block was reached, and SA patients received 10 mg of 5% hyperbaric ropicaine. Results There was no difference between two groups in the age, sex, main complications, fluid infusion and blood loss. Using univariate analysis, we found no differences between the groups in regards to MAP and HR from the beginning of anesthesia to one hour after anesthesia. In the CSA group, however, 2 patients experienced at least one episode of hypotention, while 8 patients in the SA group （P＜0.05）. In the CSA group,（5.0±0.0）mg ephedrine was injected, while（10.0±2.7）mg in the SA group（P＜0.05）. In the CSA group,（7.9±0.9）mg ropicaine was required, while 10 mg in the SA group （P＜0.05）. Conclusion In aged patients undergoing lower extremity surgery, CSA provides fewer episodes of hypotension and fewer ephedrine usage compared with SA.