Ｏｂｊｅｃｔｉｖｅ　To evaluate the effects of ketamine on remifentanil-induced postoperative hyperalgesia in patients undergoing thyroid surgery.　Methods　Forty patients scheduled to undergo thyroid surgery were randomly divided into two groups (n=20): a ketamine group and a control group. The pain thresholds were measured by von Frey filaments 24 h and 48 h after surgery. The pain intensity was evaluated 30 min, 2 h, 6 h, 12 h, 24 h and 48 h after surgery.　Results　The pain threshold in the ketamine and control groups was (4.3±0.4) g vs (3.9±0.4) g and (4.2±0.4) g vs (3.8±0.4) g at 24 h and 48 h after surgery (P<0.05), respectively. Postoperative pain intensity was similar between the two groups (P>0.05).　Conclusions　A low-dose infusion of ketamine can reduce remifentanil-induced postoperative hyperalgesia in patients undergoing thyroid surgery.