Abstract Four novel tetranortriterpenoids, xylomexicanins E–H ( 1 – 4 ), were isolated from the seeds of the Chinese mangrove, Xylocarpus granatum . Among them, xylomexicanin E ( 1 ) represents the first example of limonoid with azaspiro skeleton between B (pyrrolidine) and C rings, whose biosynthetic pathways were proposed. The structures were elucidated on the basis of one- and two-dimensional NMR (including 1 H, 13 C NMR, DEPT, 1 H– 1 H COSY, HSQC, HMBC, and NOESY) and confirmed by high-resolution mass spectrometry. Compound 2 , the second example of a limonoid with a C-9–C-30 linkage, showed moderate activity against the A549 and RERF cell line with IC 50 value of 18.83 and 15.83 μM,