Eight alkaloids were isolated and identified by natural product separation and activity tracking in order to find out the active components in Macleaya cordata that were resistant to Exserohilum turcicum.The eight alkaloids were 6-(2-hydroxyethyl)-5,6-dihydrosanguinarine (1),6-(2-methoxy-2-oxyethyl)-5,6-dihydrosanguinarine (2),6-acetodihydrosanguinarine (3),6-acetonyldihydrochelerythrine (4),isointegriamide (5),arnottianamide (6),dihydrosanguinarine (7) and chelerythrine (8).Compounds 1,2,5,6 were isolated from the stem of M. cordata for the first time.The above alkaloid compounds (1-8) were tested by agar diffusion method with filter paper.It was confirmed that compound 8 had significant biological activity against E. turcicum.Then,the IC₅₀ value of compound 8 on spore germination of E. turcicum was 12.0 μg/mL.From these results,our understanding of antifungal activity of chelerythrine against E. turcicum was enriched and this research is relevant for developing novel pesticides.