Abstract: To study alkaloid constituents in Corydalis decumbens, thirteen compounds were isolated from 95% ethanol extracts of Corydalis decumbens(Thunb)Pers. by silica gel, RP-C₁₈, Sephadex LH-20 column chromatographer, recry stallization, thin-layer chromatography and HPLC. Their structures were elucidated on the basis of spectral data combined with physiochemical properties as tetrahydropalmatine( 1 ), oxyhydrastinine( 2 ), doryanine( 3 ), palmatine( 4 ), bicuculline( 5 ), canadine( 6 ), tetrahydrocoptisine( 7 ), corydaldine( 8 ), epicorynoxidine( 9 ), N-methylcorydaldine( 10 ), (+)-corlumine( 11 ), N-methyl-6, 7-dimethoxyisoquinolone( 12 )and oxysanguinarine( 13 ). Compounds 2 , 3 , 6 , 7 , and 9 - 13 were isolated from this plant for the first time. In addition, compounds 2 , 3 , and 9 - 13 were obtained firstly from this genus. Pharmacological experiments showed that tetrahydropalmatine( 1 )might have analgesic or sedative effects, and the bicuculline( 5 )could probably induce epilepsy.