Background: The Diagnostic reference levels (DRLs) play a critical role in the optimization of radiation dose especially, in some conditions like pediatrics. They are useful indicators by which the radiologists can be aware of delivered excess radiation doses to the patients, and take corrective actions if necessary. In order to meet some requirements for establishing the national computed tomography DRLs tables, much studies are needed all around the country. Materials and Methods: All active computed tomography (CT) scanners in public and private centers in Tehran were identified and checked for quality assurance and control certification. Eleven centers were chosen to be studied according to CT examination frequencies. Weighted CT dose index (CTDIw) and dose length product (DLP) for head, sinus, chest and abdomen/pelvis scans of children were obtained from scanner’s operator consoles and classified into four groups based on their ages (A; <1 year, B; 1-5 years, C; 5-10 years and D; 10-15 years).  The 3rd quartiles of CTDIw were considered as DRLs and compared with the reported European :::union::: (EU) and United Kingdom (UK) ones. Results: DRLs for head, sinus, chest and abdomen/pelvis scans were found to be 86.76, 31.33, 6.33, 7.65 mGy; 43.38, 31.33, 6.33, 7.65 mGy; 43, 31.33, 6.33, 7.65 mGy and 44.53, 31.33, 6.33, 7.65 mGy in the four groups (A-D) respectively. They are lower than the reported DRLs in EU and UK. Conclusion: There are variations in the radiation dose between the CT centers and identical scanners indicating the necessity for dose optimization. The data reported in this study can be remarkably useful in this concern.