A new method was described which allowed the analysis of sialic acids in glycoproteins at femtomole. Sialic acids released from recombinant human erythropoietin(rhu-EPO), human urine trypsin inhibitor(h-UTI) and bovine α₁-acid glycoprotein(α₁-AGP) by acid hydrolysis, were derivatized with 2-aminoacridone(AMAC), and then separated by capillary electrophoresis, separately. The quantities of sialic acids in the first two glycoproteins were consistent with the previous results while inconsistency was found in the bovine α₁-AGP case. It was found that in bovine α₁-AGP N-glycoloyneuraminic acid (Neu5Gc) was present in addition to Neu5Ac with a quantity comparable to that of Neu5Ac. Based on these data, the AMAC-derivatized sialic acids were unstable and could undergo a decarboxylation reaction at room temperature under light, but they were stable at －20℃in the dark for at least 12 h.