Nine unprecedented diterpenoid alkaloid, including a diterpenoid alkaloid featuring a diterpenoid moiety, anthoroidine A; one bisditerpenoid alkaloid joined with a carbon-carbon single bond, anthoroidine B; three racemulosine-type C20-diterpenoid alkaloids, anthoroidines C-E; one hetidine-type C20-diterpenoid alkaloid, anthoroidine F; and three hetisine-type C20-diterpenoid alkaloids, anthoroidines G-I, together with ten known diterpenoid alkaloids were isolated from Aconitum anthoroideum DC. Their structures were established via detailed spectroscopic analyses. Most of the isolated compounds along with five known diterpenoid alkaloids obtained in a previous study were screened for neuroprotective activities and acetylcholinesterase inhibitory effects. Nominine showed potent protective activity against MPP+-induced apoptosis in SH-SY5Y cells, with a rescue rate of 34.4% (50 μM). Rotundifosine F showed a significant inhibitory activity against AChE (IC50 = 0.3 μM). The structure-activity relationship of these alkaloids is also briefly discussed.