Capilliposide B, a novel oleanane triterpenoid saponin isolated from Lysimachia capillipes Hemsl, showed significant anti-tumor activities in recent studies. To characterize the excretion of Capilliposide B, a reliable liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for simultaneous determination of Capilliposide B and its active metabolite, Capilliposide A in rat urine and feces. Sample preparation using a solid-phase extraction procedure was optimized by acidification of samples at various degrees, providing extensive sample clean-up with a high extraction recovery. In addition, rat urinary samples were pretreated with CHAPS, an anti-adsorptive agent, for overcoming nonspecific analytes adsorption during sample storage and process. The method validation was conducted over the curve range of 10.0-5000 ng/ml for both analytes. The intra- and inter-day precision and accuracy of the QC samples showed <= 11.0% RSD and -10.4-12.8% relative error. The method was successfully applied to an excretion study of Capilliposide B following intravenous administration. (C) 2016 Elsevier B.V. All rights reserved.