Fagaridine is a quaternary benzo[c]phenanthridine alkaloid, originally isolated from Fagara xanthoxyloides in 1973. The assigned structure of this alkaloid was 7-hydroxy-8-methoxy-5-methyl-2, 3-(methylenedioxy)benzo[c]phenanthridinium (1). We have synthesized this compound, coded NK109, aiming at a practical antitumor drug, and during synthetic studies we questioned the original assigned structure. Thus, we synthesized 8-hydroxy-7-methoxy-5-methyl-2, 3-(methylenedioxy)benzo[c]phenanthridinium (2), isomer of the assigned structure, and compared the spectroscopic data of both 1 and 2. The NMR data of 1 and 2 were very similar, but the UV spectra were completely different. The UV data for fagaridine agreed with these for 2; consequently, the true structure of fagaridine is 2, not 1.