Abstract Papaveraceae is one of the prominent alkaloid-containing families, and plants of the genus Glaucium (Papaveraceae) are known for their bioactive alkaloids. Glaucium species have been used in traditional medicine in Turkey as an analgesic, narcotic, sedative, and antitussive. In this study, it was planned to evaluate the inhibitory activity of an alkaloidal extract of Glaucium corniculatum subsp. refractum on acetylcholinesterase (AChE), butyrylcholinesterase (BuChE) and prolyl oligopeptidase (POP), as well as exploring the chemical profile of the plant by using Gas Chromatography-Mass Spectrometry (GC-MS). The AChE, BuChE and POP inhibition activities of the alkaloidal extract of G. corniculatum subsp. refractum were determined spectrophotometrically. A rapid GC-MS method was used to identify alkaloids that could be responsible for these inhibition activities. In total, eleven alkaloids were identified in the alkaloid extract of the plant by GC-MS. Allocyptopine (52.92%) and protopine (25.38%) were found as the major constituents. The alkaloidal extract of G. corniculatum subsp. refractum showed potent AChE inhibitory activity (IC50:1.25 µg/mL) and BuChE inhibitory activity (IC50: 7.02 µg/mL). The extract also showed a remarkable inhibitory effect on POP with an IC50 value of 123.69 µg/mL. This study presents the first GC-MS investigation and POP inhibitory activity of G. corniculatum subsp. refractum.