Berberis brandisiana Ahrendt (Berberidaceae), a shrub growing in northern Pakistan, was studied for its alkaloidal contents in aerial parts, resulting in the isolation of a new bisbenzylisoquinoline (+)-berbamine 2'-P-N-oxide (1), C₃₇H₄₀N₂O₇. The mass spectrum of 1 showed a molecular ion peak at m/z 624, with strong peaks at m/z 608 (due to loss of an oxygen atom, diagnostic of an N-oxide) and m/z 198 (corresponding to the doubly charged upper half of the m/z 608 species). Reduction of 1 with zinc in HCl afforded known (+)-berbamine. The 360 MHz (CDCl₃) NMR spectrum revealed that the 2'-N-methyl signal (δ 3.27, vs. δ 2.57 in berbamine) had a downfield shift of 0.7 ppm, and the H-1' signal (δ 4.46, vs. δ 3.85 in berbamine) had a downfield shift of 0.61 ppm, supporting a P-N-oxide configuration. NMR nOe analysis confirmed the syn relationship between the 2'-N-methyl and H-1', further establishing the 2'-P-N-oxide stereochemistry. Known alkaloids isolated from B. brandisiana included the isoquinolone thalifoline, tetrahydrobenzylisoquinoline (+)-reticuline, aporphines (+)-apoglaziovine and (+)-isoboldine, protoberberinium salts berberine and palmatine, and bisbenzylisoquinolines (+)-isotentrandrine, (+)-berbamine, and (+)-penduline. While bisbenzylisoquinolines of Berberis species usually possess the R,S' configuration (e.g., (+)-isotetrandrine, (+)-berbamine, and 1), (+)-penduline is unusual with the S,S' stereochemistry.