A method for determintion of allantion in Psammosilene tunicoides was established by HPLC. Using alcohol as the extraction solvent, the subsequent filtrate of P. tunicoides was analysed by HPLC. Allantoin was successfully detected and separated by ZORBAX NH2 column (4.6 mm x 150 mm,5 microm) at wavelength of 220 nm and column temperature of 40 degrees C, with acetonitrile-water (93: 7) as mobile phase at a flow rate of 1.0 mL x min(-1). The results showed that it had a good linear relationship between the concent ration of allantion and chromatographic peak area. The linear correlation coefficient of allantion was 0.999 5 in 0.010 4-0.166 g x L(-1). The relative standard deviation of six parallel injections was less than 2.1%. The average recoveries were ranged from 95.47% to 100.9%. This method was sensitive and accurate for the determination of allantion in P. tunicoides.