Conformational properties of rigid and semiflexible cyclic chains are still unclear owing to few experimental researches on dilute solution properties. Five cyclic amylose tris(3,5-dimethylphenylcarbamate) (cADMPC) samples ranging in the weight-average degree of polymerization from 23 to 150 were prepared from enzymatically synthesized cyclic amylose. Light scattering and small-angle X-ray scattering measurements were made on the samples to determine the weight-average molar mass Mw, the particle scattering function P(q), and the z-average mean-square radius of gyration ⟨S2⟩z in methyl acetate (MEA), 4-methyl-2-pentanone (MIBK), and tetrahydrofuran (THF) at 25 °C. The obtained P(q) and ⟨S2⟩z data were analyzed on the basis of the cyclic wormlike chain model to determine the wormlike chain parameters, that is, the helix pitch (or helix rise) per residue h and the Kuhn segment length λ–1 (the stiffness parameter or twice of the persistence length) as a function of Mw. Although the chain stiffness parameter ...