For the quality control of traditional herbal medicine, Cinnamomi Ramulus, simultaneous determination of cinnamic acid, cinnamaldehyde, and 2-methoxycinnamaldehyde was established by using a high performance liquid chromatographic (HPLC) method with diode array detector. To separate three constituents, Eclipse XDB C18 ($5{mu}m$, $4.6{ imes}250mm$) was used with 0.1% acetic acid and acetonitrile. Validation of the chromatography method was evaluated by linearity, recovery, and precision test. Calibration curve of standard components showed excellent linearity ($R^2$ >0.9999). A simple and efficient method by HPLC was developed to evaluate the quality of traditional herbal medicines made from Cinnami Ramulus. Three major bioactive ingredients in 30 samples that are from China(8) and Vietnam(22) were separated and quantified.