Purpose of the study : To compara the success rate of self-reported pain assessment in postanesthetic care unit (PACU) between conventional and structured instructions and exploring the correlation between numeric rating scale (NRS) and verbal rating scales (VRS). Methods : A randomized, contrlled trial study was performed in 110 patients, aged 10 to 70 years undergoing surgery at Srinagarind Hospital. Before starting general anesthesia, group 1 (n = 55) attended the conventional instruction and group 1 (n = 55) attended the structured instruction (an example of their pain intensity from recent intravenous cannulation). In the PACU, all extubated patients who had sedation score <3 were asked to rate their pain intensity using both VRS and NRS. The ability to rate their pain within 1 minute was defined as success. Results : All patients could report their pain using VRS. The success rate for reporting pain using NRS in group 2 was significantly higher than in group 1 (85.5% vs 63.6%,p = 0.01). There was good correlation between VRS and NRS (r = 0.69, p < 0.001). Discussion : By emphasizing and using the real example for pain assessment, the patients were able to understand more about their pain intensity. The high correlation between NRS and VRS was similar to the previous reports. Conclusion : The structured instruction can improve the success rate of self-reported pain assessment in the immediate postoperative setting. This should be included in routine preoperative visit in order to improve quality of patient care in the PACU.