Objective To study the antibacterial constituents of Senecio cannabifolius.Methods The antibacterial effect of all the extracts was tested in vitro with Staphylococcus aureus,Bacillus subtilis(Gram-positive bacilli),and Escherichia coli(Gram-negative bacillus).Chemical constituents were isolated by chromatography.Physicochemical characters and spectroscopic analyses were employed for their structural identification.Results Five compounds were isolated and their structures were elucidated by chemical and spectral methods as follows: methyl-5-hydroxy-2-pyridinecarboxylate(E-13),6-hydroxy-7,7a-dihydro-2(6H)-benzofuranone(E-14),2-(1,4-dihydroxycyclohexanyl)-acetic acid(E-16),3-hydroxycyclohexanecarboxylic acid(E-17),and 4-hydroxy benzaldehyde(B-14).Conclusion All of them are isolated from the plants of Senecio L.for the first time.