Fumaflorine (1), a new 1-benzylisoquinoline alkaloid, was isolated from the aerial parts of Fumaria densiflora. Continuing phytochemical studies on F. densiflora of Bulgarian origin, the new alkaloid fumaflorine (1) and compound (2) (molecular formula C21H17NO7) were isolated. The structure of fumaflorine (1) was determined by spectroscopic methods including EIMS, 1H-NMR, 13C-NMR, delay-COSY, and NOESY experiments, and it is the first alkaloid with a completely aromatic isoquinoline ring found in the Fumariaceae. Compound (2) was identified as the O-methyl ester of fumaflorine (1) by methylation of (1) yielding a methyl ester identical to (2) in 1H-NMR and EIMS spectra.