The current study aims to investigate the pharmacokinetic study of eight caffeic acid derivatives (forsythoside A, isoforsythoside, forsythoside B, neochlorogenic acid, chlorogenic acid, cryptochlorogenic acid, 3,5-dicaffeoylquinic acid and 3,4-dicaffeoylquinic acid) following oral administration of Flos Lonicerae-Fructus Forsythiae herb combination in rats. A rapid and sensitive ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed to determine the eight caffeic acid derivatives simultaneously in rat plasma. After mixing with the internal standard (IS) tinidazole, plasma samples were pretreated by liquid-liquid extraction with n-butyl alcohol/ethyl acetate (7:3, v/v). The separation was performed on an Acquity UPLC HSS T3 C18 column (100mm×2.1mm, 1.8μm) at a flow rate of 0.4mLmin(-1), and acetonitrile/methanol (4:1, v/v)-0.4% formic acid was used as mobile phase. The detection was performed on a triple quadrupole tandem mass spectrometer by multiple reaction monitoring (MRM) via electrospray ionization (ESI) source with positive and negative ionization modes. All calibration curves had good linearity (r>0.991) over the concentration ranges of 1.097-2246ngmL(-1) for neochlorogenic acid, 6.535-6692ngmL(-1) for chlorogenic acid, 2.103-2153ngmL(-1) for cryptochlorogenic acid, 0.5058-129.5ngmL(-1) for 3,5-dicaffeoylquinic acid, 0.3205-82.05ngmL(-1) for 3,4-dicaffeoylquinic acid, 1.002-512.8ngmL(-1) for isoforsythoside, 0.4795-982.1ngmL(-1) for forsythoside A and 0.7587-776.9ngmL(-1) for forsythoside B, respectively. The intra- and inter-batch precisions were all within 15% and the accuracy (relative error, RE%) all ranged from 85.68% to 114.7%. It was shown from pharmacokinetic parameters that the rank order of AUC0-t, Cmax and T1/2k for phenolic acids was chlorogenic acid>neochlorogenic acid≥cryptochlorogenic acid>3,4-dicaffeoylquinic acid≥3,5-dicaffeoylquinic acid (most of them had significant differences), which corresponded to their administration dosages to rats, but that of MRT0-t and T1/2z were opposite. Besides, the AUC0-t, Cmax, MRT and T1/2z except T1/2k of isoforsythoside and forsythoside B had no significant difference, compared to that of forsythoside A though their administration dosages were significantly lower than that of forsythoside A. All results showed that the method was applied to the pharmacokinetic study of the eight caffeic acid derivatives in rat plasma successfully after oral administration of Flos Lonicerae-Fructus Forsythiae herb combination, and there were significant differences of caffeic acid derivatives even isomers in the pharmacokinetic parameters.