Pinoresinol diglucoside (PD), a typical marker compound in Ecommia ulmoides Oliv., is an important and natural antihypertensive drug. A selective, sensitive, and rapid liquid chromatography tandem mass spectrometric (LC-MS/MS) analytical method was developed for the determination of PD in rats. After simple protein precipitation with acetonitrile, chromatographic separation of PD was conducted using a reversed-phase ZORBAX SB C18 analytical column (4.6mm × 150 mm, 5 μm particles) with a mobile phase of 10mM ammonium acetate-methanol-acetic acid (50:50:0.15, v/v/v) and quantified by selected reaction monitoring mode under positive electrospray ionization condition. The chromatographic run time was 3.4 min for each sample, in which the retention times of PD and the internal standard were 2.87 and 2.65 min, respectively. The calibration curves were linear over the range of 1.00~3000 ng/mL and the lower limit of quantification was 1.00 ng/mL in rat plasma. The precision expressed by relative standard deviations were <8.9% for intra-batch precision and <2.0% for inter-batch precision, and the intra- and inter-batch accuracy by relative error was within the range of -3.9% ~7.3%, which met acceptable criteria. The LC-MS/MS method was successfully applied to investigate the pharmacokinetics and oral bioavailability of PD in rats, with the bioavailability being only 2.5%.