Abstract:  By using the simulated physical digestion method of decomposing the substrates by micropopulation in half-vivo model, the biodegradabilities of cornstarches with different amylose contents and those of their modified starches were studied. The results indicate that the biodegradabilities of cornstarches and their modified starches are related to the amylose content, that the high-content amylose starch containing 50% amylose is most difficult to biodegrade, while the ordinary cornstarch (with the amylose content of 26% ) is most easy to biodegrade, and the biodegradability of the cornstarch containing 70% amylose is medium. The experimental results also indicate that the biodegradabilities of ordinary cornstarches and the cornstarches with high-content amylose decrease by cross-linking but increase by carboxyl-methvlation.