The structures and absolute configurations of four minor diterpene alkaloids in Spiraea japonica, spirasines XII [1], XIII [2], XIV [3], and XV [4], were established by spectroscopic and chemical methods. In a previous paper (1) we reported the structure of spirasine X, a diterpene alkaloid isolated from Spiraea japonica L. var. fortunei (Pl.) Rehd. (Rosaceae). We now present the structural elucidation of another four new diterpene alkaloids of this series designated as spirasines XII [1], XIII [2], XIV [3], and XV [4] isolated from the same plant. All four alkaloids have a masked keto group at C-6. N-Methylation restores the C-6 keto group, which gives rise to an acid-quenchable negative Cotton effect at about 290 nm, thus allowing the assignment of absolute configuration as shown. Then the sign of the Cotton effect at about 305 nm can be used to discriminate C-11 and C-13 carbonyl groups (2-4).