Cinnamic acid (CA), 3,4-dihydroxybenzaldehyde (3,4-DHBA), ferulic acid (FA), and 4-hydroxycynnamaldehyde (4-HCA) are the four major active ingredients of CKD-495, and it has been developed effective for the treatment of acute and chronic gastritis. However, no study has investigated the pharmacokinetic parameters of standardized Cinnamon Bark Dried Extract (CKD-495). The present study has developed and validated a simple and accurate simultaneous UPLC-MS/MS bioanalytical method of the four bioactives for evaluating the pharmacokinetics of CKD-495 in rat. The chromatographic separation was achieved using acetonitrile and 0.005% formic acid with gradient flow system on a Halo C₁₈ column. A positive electrospray ionization mode was selected to estimate m/z of CA (147.0→103.0), 3,4-DHBA (137.1→10.0), FA (193.1→134.0), 4-HCA (149.1→55.0), and internal standard (237.1→194.1), respectively. Chromatograms showed high resolution, sensitivity, and selectivity without interference by plasma constituents. The calibration curves of each analyte satisfied linearity, with correlation coefficients > 0.99. No significant interference at the retention times of the analytes was found and the within- and between-run accuracy/precision were all within the acceptance criteria. This analytical method developed in this study satisfied the criteria of international guidance. It could be successfully applied to pharmacokinetic studies of CA, 3,4-DHBA, FA, and 4-HCA after oral administration of CKD-495 to rats.