Abstract: Various types of local anesthetics have been used to achieve more appropriate postoperative consequences as well as to minimize postoperative pain severity in patients undergoing tonsillectomy surgery. It seems that adding ketamine to other local anesthetics may enhance their analgesic effects. The aim of the present study is to evaluate the analgesic effect of ketamine as an additive to bupivacaine in patients undergoing tonsillectomy surgery. This randomized double-blinded clinical trial was conducted on 63 consecutive patients aged between 4 and 30 years, belonging to ASA class I and II who were scheduled for tonsillectomy surgery. Subjects were randomly assigned to receive one of the three following anesthesia protocols: ketamine alone (0.5 mg kg^-1) bupivacaine 0.25% alone (5 mL) or ketamine (0.5 mg kg^-1) combined with bupivacaine 0.25% (5 mL). At 4 and 24 h after surgery although, no difference was observed between the two groups who received ketamine alone and bupivacaine alone, the pain severity was significantly lower in the group received ketamine combined with bupivacaine. At two time points of 4 and 24 h after surgery, the difference between the patients who received ketamine alone and bupivacaine alone was not significant but mean pulse rate in the group who received ketamine plus bupivacaine was more stable than the other two groups. No significant difference was found across the three groups in prevalence of postoperative nausea and vomiting. Mean number of hospitalization in the group which received bupivacaine alone or the group that received a combination therapy was significantly lower than that receiving only ketamine. Adding ketamine to pre-incional bupivacaine infiltration leads to reduced post operative pain when compared with use of bupivacaine alone. However, this combination therapy may not decrease the prevalence of postoperative nausea and vomiting or the length of hospital stay in the patients undergoing tonsillectomy.