We investigated the chelating effect of FeCl3 on three beta-diketones, curcumin [1], (-)-3-(trifluoroacetyl)camphor [2] and 3-formylchromone [3], as judged by changes in their cytotoxicity and absorption spectra. Addition of an equimolar concentration of FeCl3 almost completely abrogated the cytotoxicity and changed the pattern of absorption spectra (decrease in the peak height at 430 nm) of [1], without affecting those of [2] and [3]. A semiempirical molecular orbital method (CAChe), based on these experimental data, proposed the estimated structure of [1] chelated with FeCl3 at 1:1 molar ratio. The present study suggests that [1], but not [2] and [3], is an iron chelator.