2-N-methylexcentricine (2), a new alkaloid related to excentricine, was isolated together with 10 other known alkaloids from the roots of Stephania excentrica. The structure of 2 was elucidated by spectroscopic analysis. In the previous paper, we reported that excentricine (1), a new alkaloid with a novel tetrahydroisoquinoline skeleton possessing an eight-membered oxygen-heterocyclic ring, was isolated from the roots of Stephania excentrica H. S. Lo (Menispermaceae), along with eight known alkaloids. Our continuous phytochemical investigation of the roots of S. excentrica afforded 2-N-methylexcentricine (2), a new alkaloid with the same skeleton as 1, and a known alkaloid 2-N-methylcoclaurine. 2-N-methylexcentricine (2) was obtained as needles from the alkaloidal fraction of the roots by chromatography on Si gel. Its HRMS gave the molecular formula C19H25O5N. The IR, 1H- and 13C-NMR spectra were similar to those of excentricine (1), suggesting the same skeleton. The 1H-NMR spectrum of 2 showed an additional N-methyl group at δ 2.58 (3H, s) and an upfield proton at δ 4.08 (d, J = 6.0 Hz, H-1) as compared with 1. The 13C-DEPT spectrum of 2 displayed a methyl carbon at δ 36.83 (q) and a downfield carbon at δ 61.51 (d, C-1) in contrast to 1, indicating an N-methyl group in 2 instead of the NH found in 1. The CD spectrum of 2 resembled that of 1, showing the same configuration. All of the other known alkaloids were identified by comparison of their mp, [R]D (and CD), IR, UV, 1H NMR, and 13C NMR with literature data.