BACKGROUND: Although intravenous or intramuscular opioids are widely used for managing postoperative pain after cesarean section (CS), their side effects are bothering and limit their use. The aim of this study was to determine the effect of intranasal ketamine on pain intensity after CS. METHODS: In a single-center, double-blind, parallel-group, randomized controlled trial, a total of 120 patients who were scheduled for elective CS were randomly assigned into two groups. After birth, 1 mg of midazolam was administered to all patients. In addition, 1 mg/kg intranasal ketamine was administered to patients in the intervention group. For patients in control group, normal saline was administered intranasally as a placebo. The severity of pain and nausea in the two groups was evaluated after 15, 30 and 60 minutes, as well as 2, 6 and 12 hours after the initial administration of the medications. RESULTS: The trend of changes in pain intensity was decreasing and these changes were statistically significant (time effect; P<0.001). The pain intensity in the placebo group was higher than the intervention and the observed difference was statistically significant, regardless of the time studied (group effect; P<0.001). In addition, it was shown that regardless of the study group, the trend of changes in nausea severity was decreasing and these changes were statistically significant (time effect; P<0.001). Regardless of the time studied, the severity of nausea in the placebo group was higher than the intervention group (group effect; P<0.001). CONCLUSION: According to the results of this study, it seems that the using of intranasal ketamine (1 mg/kg), can be considered as an effective, well tolerated and safe method in reducing pain intensity as well as the need for postoperative opioid consumption after CS.