Paris polyphylla var is an herbal plant herb widely used in Traditional Chinese Medicine. The purpose of this study is to develop an Ultra Performance Liquid Chromatography-tandem mass spectrometer (UPLC–MS) method to quantify the major components (i.e., nine saponins) from P. polyphylla in plasma samples. A UItra BiPh column (100 × 2.1 mm, 5 μm) was used with acetonitrile/0.1% formic acid in water as mobile phases. The analytes were quantified using a Waters XEVO TQ mass spectrometer via multiple reaction monitoring (MRM) with positive scan mode. A protein precipitation method was used to extract the analytes from rat plasma. The inter/intra-day precision, accuracy, recovery, matrix effect, and stability were evaluated per the FDA guidance. The method showed linearity in the concentration ranges of 2.4–1250 ng/mL. The intra-day and inter-day precisions (RSD) of these analytes at three different levels were less than 15.0%. The extraction recoveries of these analytes were from 83.8% to 109.4% and the matrix effects ranged from 87.4% to 105.4%. The stabilities of these compounds in plasma were evaluated by analyzing three different concentrations following storage at 25 °C for 6 h, and −80 °C for 30 days. All the samples displayed less than 15.0% variations. The validated method was successfully used to a pharmacokinetic (PK) study using Sprague Dawley (SD) rats with intravenous (i.v.) and oral (p.o.) administration of P. polyphylla extract. The applications revealed that this method can be used to analyze major steroidal saponins from P. polyphylla in biological samples.