Abstract: (±)-Bicoryanhunine B (1), a new dimeric benzylisoquinoline alkaloid was isolated from the dried tubers of Corydalis yanhusuo by various chromatographic methods, including silica gel, Sephadex LH-20, reverse phase C18, and semi-preparative HPLC. Its structure was determined by spectroscopic methods, including UV, IR, ESI-MS, HR-ESI-MS and 1D/2D NMR. (±)-Bicoryanhunine B (1) was a moderate PD-1/PD-L1 interaction inhibitor with an IC₅₀value of 7.80 ±0.49 μmol·L^-1. In addition, 1 exhibited potent inhibitory activities against LPS-induced NO production in RAW 264.7 macrophages with an IC₅₀value of 4.83 ±2.21 μmol·L^-1.