In the current study, a simple ultra-high performance liquid chromatography–tandem mass spectrometry method was developed and fully validated for the quantitation of deacetyl asperulosidic acid methyl ester in rat plasma. The plasma sample was precipitated with acetonitrile and then separated on the Waters ACQUITY UPLC HSS T3 column. The mobile phases, water and acetonitrile, were added with 0.1% formic acid. The mass spectrometry detection was performed in negative-ion multiple reaction monitoring. In the range of 1–1000 ng/mL, the linearity meets the requirements with correlation coefficient more than 0.99. The parameters of accuracy, precision, carryover, matrix effect, extraction recovery, stability, and dilution integrity are within accepted ranges. The validated method has been successfully used for pharmacokinetic study of deacetyl asperulosidic acid methyl ester in rats. After oral administration, deacetyl asperulosidic acid methyl ester was quickly absorbed into blood and reached the maximum plasma drug concentration of 4047.49 ng/mL at 2 h. The half-life of deacetyl asperulosidic acid methyl ester is 5.6 h, which suggests that it has a moderate metabolic process. Since the absolute bioavailability of deacetyl asperulosidic acid methyl ester is only 3.74%, its gastrointestinal stability, first-pass effect, and transmembrane properties remain to be studied.