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Objective: A sensitive and rapid ultra‐high‐performance liquid chromatography–tandem mass spectrometry (UHPLC–MS/MS) method was successfully applied to the determination of 10 alkaloids in beagle dog plasma following a single oral dose of Xiatianwu capsules and enteric‐coated capsules, with theophylline serving as the internal standard (IS). Methods: Plasma samples were preprocessed using liquid–liquid extraction (LLE) with ethyl acetate ahead to separation using a gradient elution procedure on a Waters ACQUITY UPLC HSS T3 column (1.8 μm, 100 × 2.1 mm). The mobile phase was composed of 0.1% formic acid solution and acetonitrile at the flow rate of 0.3 ml/min. Multiple reaction monitoring (MRM) was used to determine the analytes in the positive ion mode. Results: The calibration curves for 10 analytes demonstrated a high degree of linearity (r ≥ 0.9920). The lower limit of quantification (LLOQ) values for 10 alkaloids were all more than 1.074 ng/ml, and matrix effects varied from 94.25% to 106.15%. The mean extraction recovery of quality control samples at low (LQC), medium (MQC) and high (HQC) concentrations, as well as IS, was all more than 76.60%. The intra‐day and inter‐day precision (RSD) also satisfied the requirement. Simultaneously, the variation of assay accuracies (RE) was between 13.05% and 9.38%. Conclusion: The test was validated in accordance with regulatory bioanalytical guidelines and was found to be suitable for use in a pharmacokinetic investigation of these compounds in beagle dogs after oral administration of Xiatianwu general capsules and enteric‐coated capsules. The Cmax of 10 alkaloids ranged from 52.61 to 192.46 ng/ml after oral administration of Xiatianwu capsules, and from 67.50 to 247.36 ng/ml. The Tmax was between 0.59 and 1.33 h of Xiatianwu capsules, and between 1.08 and 2.00 h of enteric‐coated capsules. The t1/2 ranged from 3.18 to 7.47 h of general capsules, and from 6.01 to 11.36 h. AUC0‐t ranged from 181.06 to 722.74 ng·h/ml of Xiatianwu capsules, and from 275.03 to 884.17 ng·h/ml of enteric‐coated capsules. The Cmax of enteric‐coated capsules were significantly increased except for tetrahydropalmatine and berberine. Tmax of general capsules were less than 1 h, and of enteric‐coated capsules were less than 2 h. The t1/2 of dehydrocorydaline, palmatine, tetrahydrojatrorrhizine, jatrorrhizine and coptisine in enteric‐coated capsules was longer than that in ordinary capsule. The AUC0‐t and AUC0‐∞ of bicuculline, dehydrocorydaline, protopine, magnoflorine, tetrahydrojatrorrhizine, jatrorrhizine, berberine and coptisine were all significantly higher in enteric‐coated capsules. [ABSTRACT FROM AUTHOR]