Pyrrolizidine alkaloids (PAs) are hepatotoxins found in a wide variety of plant species, especially Senecio (Asteraceae), and have received extensive chemical and biological investigations because they presumably serve as protective chemicals for the plants and are the cause of considerable livestock poisoning. As the most characteristic secondary metabolites of Senecio species, large numbers of pyrrolizidine alkaloids have been isolated from this genus. Senecio vulgaris Linn., a widespread problematic weed originally from Europe and introduced to most areas of the world in the nineteenth century, has been extensively investigated for its PAs. In the course of phytochemical investigations of Senecio species distributing in northeast China, a new pyrrolizidine alkaloid, named vulgarine (1), and a known one, senecionine (2), have been isolated from the less polar extracts of S. vulgaris. This paper deals with the isolation and structure elucidation of the new pyrrolizidine alkaloid. Compound 1 was obtained as a colorless oil. Its structure was elucidated using spectral data including IR (showing carbonyl at 1711 cm⁻¹ and double bond at 1643 cm⁻¹), UV (maximum absorption at 249 nm indicating conjugated carbonyl and double bond), HRESIMS (quasi molecular ion peak at m/z 228.1226 [M+H]⁺, implying molecular formula C₁₁H₁₇NO₄), ¹H and ¹³C NMR (DEPT) (revealing three methoxy groups, a carbonyl group, a trisubstituted double bond, an oxygenated methine, and three methylenes), HMBC (confirming positions of double bond, carbonyl, and methoxy groups), and NOESY (indicating cis-configuration of two methoxy groups). Considering the β-configuration of oxygenated substituents at C-7 in S. vulgaris PAs, the structure of 1 was established as a pyrrolizidine alkaloid and named vulgarine.