Midazolam, a water soluble benzodiazepine, was compared with diazepam as the changes of eardiopulmonary function during sedation under the spinal anesthesia in elderly patients. The results were as follows; I) Cardiovascular effect. At the conclusion after diazepam 0.05 mg/kg(Group D) or midazolam 0.02 mg/kg(Group M) injection, systolic, diastolic pressure and heart rate were significantly decreased(P<0.05) in the both group from 3 min to 30 min, but maintained within normal range. However, it is not significant difference that each group. 2) Respiratory effect. SaO decreased significantly at 3 min. in M-group after midazolam injection but there was not significant difference from change in D-group. Respiratory rate, pH and PaCO2 were not significantly changed between D-group and M-group. However, PaO2 was significantly decreased(p<0.05) within normal range at 3 min. in M-group after midazolam IV and significant difference between both groups. From the above results, We have concluded that IV administration of small dose of diazepam or midaaolam during spinal anesthesia had a little changed in cardiopulmonary function. However, sedative effect was efficient.