A high sensitive and rapid method was developed for the analysis of lappaconitine in mouse plasma using liquid chromatography coupled to mass spectrometry (LC-MS).  Detection was performed by positive ion electrospray ionization (ESI) in multiple reaction monitoring (MRM) mode, monitoring the transitions m/z 585 → m/z 535 and m/z 356 → m/z 192, for the quantification of lappaconitine and tetrahydropalmatine (internal standard, IS), respectively.  The method was linear over the concentration range of 3.0−2 000.0 ng·mL⁻¹.  The lower limit of quantification was 3.0 ng·mL⁻¹.  Intra- and inter-run precisions (RSD) were both less than 9.9% and accuracy (RE) within ± 4.8%.  After single intravenous injections of lappaconitine hydrobromide at 1.0, 2.0 and 4.0 mg·kg⁻¹, the elimination half-lives (t_1/2) were 0.47, 0.48 and 0.49 h, and the areas under the curve (AUC_0−t) were 55.5, 110.5 and 402.9 ng·h·mL⁻¹, separately.  The pharmacokinetic profile of lappaconitine was linear at relatively lower dose levels (1.0−2.0 mg·kg⁻¹).  When the dose increased farther to 4.0 mg·kg⁻¹, the V_z and CL decreased, and the increase fold of the AUC was much larger than that of the dose.