The analgesic effect of epidural pentazocine for the postoperative pain relief was studied. In our previous report, we used the pentazocine diluted to normal saline, however in this study, pentazocine was diluted with distilled water and made to 10ml mixture. Fourty patients were divided into four groups (n=10) as follows: Group I: control, distilled water of 10 ml, Group II: pentazocine 0.2 mg/kg, Group III: pentazocine 0. 3mg/kg, Group IV: pentazocine 0.4mg/kg, all pentazocine groups were diluted to 10ml of distilled water. We have carried out the study to see the effects on the time of peak analgesia, the duration of analgesia, the degree of analgesia and the side effects. The results are as follows: 1) Seven cases (70%) in the control group showed rapid but short duration of analgesia. 2) The pentazocine 0.3 and 0.4 mg/kg groups were significantly different from the control group (p< 0.05). 3) In the pentazocine 0.3 and 0.4 mg/kg groups, the time of peak analgesia occured 8-9 minutes, the duration of analgesia was 10 hours and the degree of analgesia showed moderate to good degree. 4) Nine cases (90%) in the control group complained of back pain during epidural injection and 16 cases (53%) in the pentazocine group conplained of drowsiness.