Domoic acid, a main component of amnesic shellfish toxin (one of the four sorts of marine red tide bio-toxins) was determined by capillary electrophoresis with UV detection. The shellfish samples were prepared by solvent extraction, cleaned-up with a strong anion-exchange cartridge (SAX: Part No. 1210-2044, Lot No. 182639, Varian) and a cation-exchange cartridge (SCX: Part No. 1211-3039, Lot No. 171069, Varian). The quantitative analysis was performed with external standard under the optimum conditions of capillary electrophoretic analysis. The calibration curve of domoic acid showed good linearity in the range of 0.2 mg/L-50 mg/L with r = 0.9990, and the detection limit was 0.063 mg/L(S/N > 3). Spiked with standard at three levels (5.00 micrograms/g, 10.00 micrograms/g and 20 micrograms/g), the samples had the recoveries of 97.24%, 96.92% and 97.55%, and the RSDs of 2.74%, 2.59% and 1.95%, respectively. Five kinds of shellfish samples normally consumed in Dalian sea area were collected and quantified. The method has the advantages of being simple, convenient, sensitive and low cost. Therefore it can be used as one of the routine monitoring methods for amnesic shellfish toxin.