Objective To analyze the structure of degradation product of 1-cyano-4-dimethylamino-pyridinium(CDAP), a polysaccharide activator. Methods CDAP was degraded with heavy water overnight(pH 9. 0), of which the structural change before and after degradation was analyzed by UV spectroscopy(200 ∼ 400 nm), ∼1H-NMR and ∼(13)C-NMR, and the degradation level was calculated by external standard method. Results The structure of degradation product of CDAP under basic environment was consistent with that of mainly 4-dimethylaminopyridine(DMAP), while the degradation level was more than 99. 5%. Conclusion The degradation praduct of CDAP was mainly DMAP. The anal. of DMAP should be included into the test for residues during production of CDAP activation-based polysaccharide-protein conjugate vaccine.