Small-angle X-ray scattering measurements were made for cellulose, amylose, and amylose tris(ethylcarbamate) (ATEC) in an ionic liquid [1-butyl-3-methylimidazolium chloride (BnlimC1)] at 25 degrees C to determine z average mean-square radius of gyration (S-2)(z) and the particle scattering function P(q). The obtained data were analyzed in terms of the wormlike chain model to estimate the Kuhn segment length lambda(-1) (the stiffness parameter, equivalent to twice of the persistence length) and the helix pitch (or helix rise) per residue h. The chain stiffness (lambda(-1)) was determined to be 7 +/- 1 nm for cellulose, 3.5 +/- 0.5 nm for amylose, and 7.5 +/- 0.5 nm for ATEC. These values are almost the same or somewhat smaller than those of previously investigated systems, indicating these polymers have relatively high flexibility in the ionic liquid. It is reasonable to suppose that disruption of intramolecular hydrogen bonds of polysaccharide makes the main chain rather flexible in the ionic liquid.