Abstract: Aqueous solutions contained N diisopropyloxyphosphoryl amino acids (DIPP AA) and β cyclodextrin ( β CD) were analyzed by use of electrospray ion trap mass spectrometry (ESI MS) in conjunction with tandem mass spectrometry (MS/MS). The result showed that β CD could catalyze hydrolysis reaction of DIPP AA to free amino acid (AA). DIPP AA could form β CD/DIPP AA complex with β CD in the aqueous solution. The hydrolysis products were also observed to form the single charged 1∶1 ( β CD/AA) complexes. They not only had some similar cleavage patterns, but also had their similar characteristic fragment ions. The catalyzed mechanism of hydrolysis reaction was assumed by the result.