Abstract: A high performance liquid chromatography (HPLC) method was developed for the determination of three components, namely, gallic acid, epigallocatechin gallate (EGCG), and epicatechin gallate (ECG), in the polyphenolic extract of Cinnamomum cassia . The HPLC method was performed using a Kromasil 100-3.5 C₁₈ column (4.6 mm×150 mm) with mobile phases consisting of 0.2% trifluoroacetic acid aqueous solution (A) and methanol-aqueous solution (80:20) (B) with gradient elution (30%-80% B). The flow rate was set at 1.0 mL/min, and the detection wavelength was 278 nm. The intraday precision of the method was found to be less than 0.3%. The linear correlation coefficients of gallic acid (0.359-368 μg/mL), EGCG (0.629-629 μg/mL), and ECG (1.02-1041 μg/mL) in their respective concentration ranges could reach 0.9999, and the detection limits of the three components were 0.07, 0.17 and 0.26 μg/mL, respectively. The method was applied to determine two actual samples of cinnamon polyphenol extract with similar total phenol content, revealing significant differences in their compositions. This analytical method is simple to operate, precise, and reliable, making it suitable for the analysis of the composition of cinnamon polyphenolic extracts and the quantitative determination of the three polyphenolic components in cinnamon polyphenol extract.