Chiral recognition in host–guest complexations between crown ether hosts (H) and amino acid ester ammonium ion guests (G+) has been evaluated by fast atom bombardment (FAB) mass spectrometry (m-nitrobenzyl alcohol matrix). The method uses a 1/1 mixed (for example, GR + and GS–dn +) solution of the guest whose enantiomer is isotopically (deuterium) labeled. Chiral recognition of a given host is simply measured with a given guest from the peak intensity ratio of the two diastereomeric host–guest complex ions as I[(H + GR)+]/I[(H + Gs–dn)+] ≡ IR/IS–dn . Both the degree and the direction of chiral recognition are characterized by the IR/Is–dn values in the range from 0.5 to 5.4 (IR/IS-d3 ) for the present host-guest combination systems studied. Among several synthetic chiral crown ethers and related natural host compounds, it has been found that host 5 possesses remarkably large guest dependence upon the chiral recognition properties: (1) toward primary amino acid ester guests 14–21, a high degree of (R)-enantiomer preference (IR/IS = 3.2–5.4), (2) toward phenylglycine ester guest 22, almost no enantiomer recognition (IR/IS = 1.1), and (3) toward secondary amino acid ester guest 24, a weak (S)-enantiomer preference (IR/IS = 0.7). It is also shown that the IR/IS values measured with the present concentrations are reasonably correlated with the relative thermodynamic stabilities in the corresponding host-guest equilibria in solution (IR/IS ≤ KR/KS) for three typical host–guest combination systems selected (1–22, 4–16, and 5–16). Accordingly, the present FABMS/EL (enantiomer-labeled guest) method can be proposed as a new and practically useful technique for determining chiral recognition properties in the highly structured chiral host–chiral guest complexations.