Naturally available monosaccharides, D-mannose, D-galactose and D-glucose, have been used for the first time as chiral co-matrices for chiral recognition of alpha-phenylethylamine, The liquid secondary ion (LSI) mass spectra of a mixture of D-mannose and (R)- or (S)-alpha-phenylethylamine in the presence of benzylamine as reference compound and glycerol as matrix showed [(mannose + (R)- / (S)-alpha-phenylethylamine + H) - H(2)O](+) (a) and [(mannose + benzylamine + H)-H(2)O](+) (b) ions. The significant difference was observed in the relative peak intensity (RPI) values calculated from the ion abundances of ion a and b. The RPI values for (R)- and (S)-alpha-phenylethylamine are RPI(R) = 0.79 and RPI(S) = 1.34, respectively. The efficiency of the chiral recognition property of D-mannose is demonstrated in estimating the enantiomeric excess of alpha-phenylethylamine.