The new modified eremophilanes hastatusins A-K (1-11) and 13 known compounds (12-24) were isolated from Parasenecio hastatus. The structures of 1-24 were elucidated based on spectroscopic data analysis and comparison with literature data. The absolute configurations of compounds 1 and 2 were defined by single-crystal X-ray diffraction analysis, and the other new compounds were assigned based on ECD data. This work is the first report of the crystal structure of an 8,9-seco-eremophilanolide (1) with two lactone units. The enantiomers of 1 were separated by chiral-phase HPLC, and the absolute configurations of (-)-1 and (+)-1 were established via experimental and calculated ECD data. The new compounds represent four unusual skeletons: a modified 8,9-seco-eremophilane featuring a rare 6,9;8,12-dilactone moiety (1), a furanoeremophilane-type skeleton (2-7, 11), a rare C14 nor-eremophilane-type skeleton (8, 9), and a modified eremophilane lactone-type skeleton (10). All isolates were assayed for their neuroprotective effects against H2O2-induced SH-SY5Y cell injury, and compounds 2-5, 12, 21, and 23 exhibited activities even at a low concentration of 1 μM. Compounds 6-9, 13, 14, 17, 20, 22, and 24 also showed notable effects at 10 and 100 μM.