After the derivatization reaction of 8 kinds of essential amino acids(threonine,valine,methionine,isoleucine,leucine,phenylalanine,lysine,tryptophan) in human body with o-phthalaldehyde(OPA),a method of capillary electrophoresis coupled with electrochemical detection(CE-ED) was established for the determination of these eight essential amino-acids.Effects of derivatization time,detection potential,concentration and pH value of running buffer,separation voltage and injection time on the detection were investigated.Under the optimum conditions,a good baseline separation and highly sensitive detection for eight essential amino-acid in yam were achieved in 12 min.The calibration curves of eight essential amino acids were linear in the range of 0.1-1 500 μg/L,with detection limits(S/N=3) of 0.01-0.05 μg/L.The relative standard deviations(RSDs) for peak heights of eight essential amino-acids were in the range of 1.3%-1.8%,and the RSDs for migration times were 0.6%-1.0%.The method was successfully applied in the assay of eight essential amino-acids in samples of yam,with spiked recoveries of 96.8%-102.0% and RSDs not more than 2.4%.