Fentanyl is an opioid narcotic analgesic that is about 50-100 times stronger than morphine, and one of its analogues, carfentanil, is estimated to be 10,000 times more potent. Fentanyl and its analogues, like opioids such as morphine, and codeine, have the potential to abuse prescription fentanyl or misuse illegally manufactured fentanyl analogues. Therefore, numerous fatal overdose have been reported worldwide, particularly in the North American continent. However, recently in Korea, social problems caused by misuse of fentanyl have become an issue, and countermeasures are needed. Considering this, it is necessary to establish an analytical method that can detect trace amounts of fentanyl analogues that have been illegally added to foods and drugs. In this study, an LC-MS/MS method was developed to screen and quantify 61 types of fentanyl analogues among illegal fentanyl substances published by the United Nations/International Narcotics Control Board (UN-INCB) in pharmaceutical patch formulations. Sample preparation was optimized with salting-out assisted liquid-liquid extraction (SALLE), and a phenyl hexyl column was used as the HPLC analytical column. The analytical method validation parameters were selectivity, linearity, limit of quantitation, accuracy, precision, and carryover in accordance with the guidelines from the Ministry of Food and Drug Safety (MFDS) in Korea. In addition, peak purity analysis was performed using HPLC-DAD on the fentanyl analog synthetic standards provided by the synthesis research team to confirm the presence of impurities, thereby improving the accuracy and reliability of the analysis. The developed analytical method will contribute to the regulation and monitoring of illegal fentanyl analogues in the future. This research was supported by a grant (21202분석연309-3) from Ministry of Food and Drug Safety in 2022.