To improve the color stability of the bioplastic containing sorghum extract, sorghum extract was chelated by ametal ion. The chelating activity was quantitatively evaluated under the various conditions. Chelation of sorghum extract byCu(II) was determined by reaction with pyrocatechol violet, whereas Fe(II) chelation was investigated by forming complexeswith ferrozine. Chelation of sorghum extract was increased rapidly with increasing concentrations of metal salt and sorghumextract. At a 0.1g/L metal salt addition level, the chelating activity of Fe(II) and Cu(II) were 66.7% and 54.2%, respectively. According to the chelation pH conditions, the sorghum extract was chelated almost 100% by Fe(II) above the pH 6.5. It wasconfirmed that Fe(II) was a strong chelator of sorghum extract than Cu(II). The sorghum extract chelated with metal salt exhibithigher thermal stability. The bioplastic containing chelated sorghum extract showed relatively less color change than the control.