The objective of this study was to assess theintraoperative pain relief of intraperitoneallidocaine, intramuscular morphine or both in postpartumtubal ligation. As factorial designed,80 patients were randomlyallocated into 4 groups to have no medication (groupI), 10 mg of intramuscular morphine (group II), 0.5%lidocaine 80 ml. Instilled into intraperitoneal cavity(group III), and both intramuscular morphine andintraperitoneal lidocaine (group IV). Every patient had1% lidocaine 20 ml. For local sking infiltration. Numerical Rating Scale (NRS) 0-10 (O means nopain at all, 10 means the most possible pain) was ratedby the patients during the operation. Rescued drugs(fentanyl, ketamine) were used if NRS 3. The mean NRSscores were 7.30,7.60, 2.70, and 1.55 in group I, II,III and IV respectively. There were significantdifferences in NRS scores between Group I or IIcompared to group III or IV (P 0.001) but there were nosignificant differences between group I and group II orgroup III and group IV. Rescued drugs were used more ingroup I, II than group III, IV (16:16:4:2)(P 0.001).There were no significant differences in hemodynamicchanges. The mean highest lidocaine level was 2.67gm/ml. which was low as compared to the toxic level(9-10 gm/ml.). By cost effectiveness analysis, usingintraperitoneal lidocaine cost 25.50 baht more to getone patient free from severe pain during the operationas compared to intramuscular morphine. This study shows that lidocaine instillation isan effective method for pain relief in postpartum tuballigation while intramuscular is not, and lidocaineinstillation is a good canonical and safe technique forintraoperative pain relief in postpartum tuballigation.