Introduction: Renal colic refers to one or more acute and painful short-term attacks due to the movement and excretion of kidney stones. The aim of this study was to determine the effect of intravenous morphine and inhaled morphine on pain relief in renal colic patients. Methods: This clinical trial study was performed on 50 patients of Shahid Sadoghi Hospital and Shahid Rahnemoon Hospital with renal colic symptoms who were randomly divided into two groups. The first group received 5 mg intravenous morphine and 5 cc normal saline (placebo) and the second group received 10 mg inhaled morphine and 5 cc normal saline. Severity of pain was assessed at the time of emergency and onset of Visual Analog Scale and then questionnaires were completed at 10, 20 and 30 minutes intervals. The data through SPSS Inc., Chicago, IL; Version 16 and the Friedman, Mann-Whitney, and Chi-square tests were analyzed. Results: Our study showed the mean intensity of pain was 9. 52± 1. 12 (nebulized) and 9. 24± 1. 51 (intravenous) on admission without significant difference (p=0. 46). After 10 minutes, mean pain intensity in both nebulized and intravenous groups was 7. 76± 1. 3 and 6. 68± 2. 03, respectively. There was a significant difference between the two groups (p=0. 03). After 20 minutes, the mean pain intensity was 5. 68± 1. 72 and 4. 32± 2. 17, respectively, and the difference between the two groups was significant. After 30 minutes, the mean intensity of pain in two groups of nebulized and intravenous was 3. 88± 3. 14 and 3. 36± 3. 34, respectively. The difference between the two groups was not significant (p = 0. 57). The mean pain intensity in the intravenous method was lower than the nebulized, but in the nebulized method it was showed a decreasing trend. Conclusion: Nebulized morphine relieves pain in the patients with renal colic, but pain relief is faster by intravenous morphine. Accordingly, this method is more preferred in renal colic patients.