OBJECTIVE： To study the pharmacokinetics and absolute bioavailability of oleanolic acid and its derivative dihydrooleanolic acid in rats in vivo. METHODS： 12 SD rats were randomly divided into oleanolic acid administration group and dihydrooleanolic acid administration group， 6 in each group. All rats were intragastrically given related medicine （50 mg/kg）， then intravenously injected related medicine （2 mg/kg） in tail vein after 1 week. Sample blood 0.3 mL was taken from tail vein before administration and after administration （0.1， 0.25， 0.5， 0.75， 1， 1.5， 2， 3， 5， 7， 9， 12 h for ig； 0.05， 0.15， 0.25， 0.5， 0.75， 1， 2， 3， 5， 7， 9， 12 h for iv）. UPLC-QTOF was conducted to determine the plasma concentration， and DAS 2.0 pharmacokinetic software was used to calculate pharmacokinetic parameters and absolute bioavailability. RESULTS： After ig and iv oleanolic acid， the AUC0-∞ were （232.10±7.17）， （1 203.99±19.65） ng·h/mL， t1/2 were （1.75±0.10）， （1.41±0.04） h respectively； after ig， cmax was （121.3±18.92） ng/mL， tmax was （0.54±0.10） h， absolute bioavailability was 0.77％. After ig and iv dihydrooleanolic acid， AUC0-∞ were （382.03±23.73）， （386.14±10.65） ng·h/mL， t1/2 were （2.47±0.45）， （1.44±0.03） h； after ig， cmax was （124.52±12.28） ng/mL， tmax was （0.63±0.14） h， absolute bioavailability was 3.96％. CONCLUSIONS： The absolute bioavailability of dihydrooleanolic acid is significantly higher than oleanolic acid in rats.