A new naturally occurring lycoctonine-type C19-diterpenoid alkaloid aemulansine (1), together with ten known alkaloids (2-11), were isolated from the whole herb of Delphinium aemulans Navski. Their structures were elucidated by extensive spectroscopic analyses, including 1D, 2D NMR and HR-ESI-MS. Compounds 1-10 were also evaluated in vitro for cytotoxicity against A549, Hela and MCF-7 cells using the MTT method. © 2018 Natural Product Incorporation.