A simple accurate HPLC method was developed for determining the ferulic acid content in Cyperus rotundus rhizomes. The chromatographic system was equipped with a Kromasil C 18 (150 mm × 4.6 mm, 5 mm) column and UV detector set at 320 nm, in conjunction with a mobile phase of methanol and water containing 1% (v/v) acetic acid in a ratio of 30:70, at a flow rate of 1.0 ml/min. The method was examined in linearity, precision, stability, repeatability, and recovery. The retention time for ferulic acid was found to be 12.308 min; the linearity was within the range from 0.0162 to 0.162 mg, with the correlation coefficient (R) amounting to 0.9996, and the average percentage recovery was 98.75%. Employing this method, the ferulic acid content of the Cyperus rotundus, collected from twelve source areas in China, was measured, the content varying in a range of 0.027-0.0462%. Due to its accuracy and rapidness, this method can serve as an effective way for evaluating the quality of Cyperus rotundus.