Background: This study aimed to determine drug resistance mutations in patients with virological failure and find correlation between HIV drug resistance test and viral load. Methods: Blood sample was collected from 51 patients who suspicious treatment failure in the center of Imam KHO-meini Hospital, Tehran, Iran in 2015. Viral voluntary counseling and testing load test was done and the patients with viral load above 1000 copies choose for detection of drug resistance mutations by genotyping method (29 patients). Results: The majority of patients (82. 75) harbored the HIV subtype CRF 35 A-D. The 86. 2% patients compromised at least one resistance mutation. The analysis of reverse transcriptase showed M184V (68. 9%), T215YISF (44. 8%), K103N (27. 6%) and the analysis results of protease revealed G73SC (13. 8%) and I47VA (6. 9%). Eventually, the signif-icant correlation between viral load and drug resistance was found. Conclusion: The result of our research stress the significance of recognizing drug resistant on time that prohibits the accumulation of drug resistance mutation and circulates the resistance strain of HIV-1 virus and the importance of national study according to the reliable findings for treatment guidelines.