Pseudolaric acid A, a Hsp90 inhibitor with an IC50 of 0.60 μM, 2.72 μM, 1.36 μM, 2.92 μM and 6.16 μM in HL-60, A549, SMMC-7721, HeLa and SW480 cells respectively, is the main bioactive ingredient in Pseudolarix cortex, and induces cell cycle arrest at G2/M phase and promotes cell death through caspase-8/caspase-3 pathway, demonstrating potent antiproliferation and anticancer activities.