Two dimeric diterpenoids, taxodikaloid A (1) and B (2), have been identified from the seeds of Taxodium ascendens. The diterpenoid structures were established based on comprehensive spectroscopic analysis, and the absolute configuration of taxodikaloid A (1) was further confirmed by single crystal X-ray diffraction. Both structures feature an unprecedented ox-azoline ring linkage connecting two abietane diterpenoid monomers. A plausible biosynthetic pathway for compounds 1 and 2 is proposed. Both compounds show potential neuroprotective activity against Aβ25–35-induced damage in SH-SY5Y cells.