Nine new norditerpenoids and dinorditerpenoids, 2-oxonagilactone A (1), 7β-hydroxynagilactone D (2), nagilactones K and L (3 and 4), 3β-hydroxynagilactone L (5), 2β-hydroxynagilactone L (6), 3-epi-15-hydroxynagilactone D (7), 1α-chloro-2β,3β,15-trihydroxynagilactone L (8), and 15-hydroxynagilactone L (9), were isolated from the seeds of Podocarpus nagi, along with eight known analogues. The structures of the new compounds were established based on detailed NMR and HRESIMS analysis, as well as from their ECD spectra. The absolute configuration of the known compound 1-deoxy-2α-hydroxynagilactone A (16) was confirmed by single-crystal X-ray diffraction. All of the isolates were tested for their cytotoxic activities against cancer cells. The results indicated that compounds 4 and 6, as well as several known compounds, displayed cytotoxicity against A2780 and HEY cancer cells. Among the new compounds, 2β-hydroxynagilactone L (6) showed IC50 values of less than 2.5 μM against the two cell lines used. Furthermore, compound 6 induced autophagic flux in A2780 cells, as evidenced by an enhanced expression level of the autophagy marker phosphatidylethanolamine-modified microtubule-associated protein light-chain 3 (LC3-II) and increased mRFP-GFP-LC3 puncta. Also, compound 6 activated the c-Jun N-terminal kinase (JNK) pathway, while pretreatment with the JNK inhibitor SP600125 decreased compound 6-induced autophagy.