An angiotensin-converting enzyme (ACE) inhibitor, nicotianamine, was purified from Hayatouri (Sechium edule) by using some ion-exchange column chromatographies. Crystal of nicotianamine (19.8 mg) was finally obtained from 75 kg of Hayatouri. The chemical identification by IR, NMR and MS spectral analysis were carried out, and the data agreed with those of nicotianamine reported by Kristensen et al. The quantitative analytical method of nicotianamine in various resources was established by using the isolated nicotianamine. An ion-pair chromatography of reversed-phase HPLC with 0.1 mol/L SDS elution buffer (pH 2.6) afforded good separation and linearity of calibration curve when o-phthalaldehyde was used for labeled reagent for fluorescence detection. Concentrations of nicotianamine in various vegetables were determined by this method. Nicotianamine concentrations of Hayatouri (Sechium edule), Seri (Oenanthe javanica), Ashitaba (Angelica keiskei), Moroheiya (Corchorus olitorius), Kureson (Nasturtium officinale), Nigauri (Momordica charantia), Soybean (Glycine max) and Soybean milk were determined to be 0.010±0.0014, 0.012±0.0028, 0.017±0.0028, 0.022±0.0021, 0.037±0.0035, 0.015±0.0021, 0.074±0.0106 and 0.090±0.0106 mg/g, respectively. As we have established the method of nicotianamine quantitative analysis, we are planning and starting the study of absorption of this compound into the blood from the intestine and about the effect on renin-angiotensin system of hypertension.