A phytochemical investigation on chemical constituents from the rhizomes of Menispermum dauricum DC. identified eight undescribed dimeric alkaloids with structurally diverse monomeric isoquinoline. Alkaloid structures were elucidated by a combination of spectroscopic data analyses and time-dependent density functional theory (TDDFT) ECD calculation. The isolates were evaluated for inhibitory effect on dopamine D1 receptor and compound 1 exhibited potent D1 receptor antagonistic activity with an IC50 value of 8.4 ± 2.0 μM. © 2021