Purpose　The aim is to develop a method for the analysis of micro-scale amino acids in biological samples.Methods　After having been extracted and dried,the residues were dissolved in a running buffer or a distilled water and acetonitrile.The samples were loaded into column for 5,25 or 50s at a hydrodynamic injection and were separated by capillary electrophoresis.The effect of different dissolvent on the sample stacking was observed.Results　A 100-fold improvement in the amount of material that can be injected into a capillary column without loss of resolution was shown.Conclusion　The marked effect of sample stacking was achieved by the using distilled water and acetonitrile(1∶1,v/v) as dissolvent.