Corn starches with different amylose contents were enzymatically modified using Thermus aquaticus 4-$alpha$-glucanotransferase ($TA{alpha}GTase$). Upon the enzyme treatment, the chain-length distributions of isoamylolytically debranched products became broader [degree of polymerization (DP): 3-40] than those of untreated corn starches. In addition, a variety of cycloamyloses (CAs) with different sizes were formed by the glucanotransfer activity of $TA{alpha}GTase$. CAs with DP 5-40 were detectable in all of the $TA{alpha}GTase$-treated corn starches. From the results of high-performance anion-exchange chromatography and high-performance size-exclusion chromatography analyses, it was suggested that the amount of CAs produced by the enzyme treatment increased as the amylose content of the starches increased. Thus, we concluded that the extent of modification of starch molecules was enhanced in proportion to amylose content by the transfer activity of $TA{alpha}GTase$. This finding could be useful for developing an efficient process of CA production using this enzyme.