It has recently been discovered that cycloamylose, cyclic alpha-1,4-glucan with a degree of polymerization ranging from 17 to several hundred, can be produced by the action of potato D-enzyme (EC 2.4.1.25) on amylose. To obtain structural insights into this new series of cycloamylose, the topological aspects of its circular structure were discussed in terms of a ribbon model properly introduced. A simple analysis of the chain-length dependence of the product population was performed on the basis of an elastic wire model. If the amylose chain is rather stiff, a double-helical structure with foldbacks is more reasonable than a circularized single-helical structure. This is because theoretical calculations for the latter predict a periodic population oscillation, which is caused by the need for the helix ends to meet, whereas such an oscillation was not experimentally observed. However, due to the unknown chain stiffness, it is difficult to draw a definite conclusion. To answer some questions that arose in the above analysis, atomistic models are necessary. Therefore, crude atomistic models were created in close analogy with the modeling of supercoiled DNA. The models were then refined by molecular dynamics simulation performed with a fast multipole method. Both structures formed a hollow tube with internal diameter of 5-6 Angstrom. As far as the enthalpic contribution is concerned, the simulation results support the double-helical structure. The simulation results also indicated appreciable chain flexibility, which might play an important role in accommodating guest molecules.