Abstract: A recent feature of global drug markets is the unprecedented pace at which new psychoactive substances (NPS) have been developed and emerged worldwide. Synthetic opioids represent a class of NPS, which mostly consist of the prescription drug fentanyl and its analogues. Use of illicitly manufactured fentanyl and its analogues amplifies the hazards because lack of quality control for these products, which are not portioned in precise doses, and can be deadly in minuscule amounts due to the extreme potencies. The mass-spectral fragmentations of these compounds following electron ionization (EI) and electrospray ionization (ESI) under collision-induced dissociation (CID) mode were studied to obtain the fragmentation characteristics of fentanyl analogues. Compounds were analyzed on Aglient DB-5MS column (30 m×0.25 mm×0.25 μm) with an initial temperature of 60 ℃ for gradient increased temperature by GC/MS, and Acquity UPLC CSH^TM C18 column (10 cm×2.1 mm×1.7 μm) with 0.1% formic acid aqueous solution (A)-acetonitrile (B) as mobile phase for gradient elution by UPLC-Q-TOF MS. According to the structure and the typical fragmentations, these compounds could be easily identified. The countless possibilities to create new fentanyl analogues by small changes in chemical structures pose a growing challenge to forensic analysts. So this work will be helpful to assist forensic laboratories in identifying these kinds of compounds or other substances with similar structure in case work.