A new secoberbine alkaloid (-)-N-methylcorydalisol was isolated from the aerial parts of Hypecoum lactiflorum Kar. et Kir. Pazij. (Papaveraceae) of Mongolian origin and was characterised. The known alkaloids of protopine and protoberberine type protopine, allocryptopine, (-)-N-methylcanadine and (-)-N-methylstylopine were also isolated. (-)-N-methylstylopine is a new alkaloid for the genus, while (-)-N-methylcanadine is new for the species. All structures were established by physical and spectral analysis.