Objective To identify the constituents and metabolites of epimedium in rat plasma by rapid-resolution liquid chromatography-time of flight mass spectrometry (RRLC-TOF/MS) after intragastric administration, so as to explore the active ingredients and metabolites of epimedium in vivo. Methods The separation was performed on a SHISEIDO MG C₁₈ reverse phase column (3.0 mm×100 mm,3 μm)．The mobile phase consisted of water containing 0.1% formic acid and acetonitrile was used as gradient elute．The flow rate was 0.6 mL/min, post-column split ratio was 31, and the temperature of column was 25℃. Time-of-flight mass spectrometer(TOF/MS) and electrospray ion source (ESI) were applied for qualitative analysis under positive ion mode, with the mass scan range being m/z 100-1 000. Results Three prototype constituents and 4 metabolites of epimedium were identified in rat plasma. Conclusion A rapid and efficient RRLC-TOF/MS method has been established for studying the constituents and metabolites of epimedium in vivo, which provides a reference for further pharmacodynamics experiments.