Curdlan dissolved in alkaline solution forms a unique gel consisting of liquid crystalline gel (LCG) and amorphous gel (AG) in alternating layers by a dialysis into aqueous calcium chloride. The unique structure has been investigated by measuring the birefringence of the gel Delta n, the ratio q of the thickness of LCG layer delta to the gel radius R, and the calcium content in the gel C-Ca in a wide range of molecular weights of fractionated Curdlan, as well as unfractionated Curdlan as a control. With increasing molecular weight of Curdlan, Delta n increased and q = delta/R decreased, and both became saturated at high molecular weight. Delta n and q for unfractionated Curdlan were smaller and larger, respectively, than those for fractionated Curdlan. C-Ca was constant irrespective of molecular weight and its distribution, which means that the abundance of calcium ions per glucose unit in the gel does not depend on the degree of orientation of mesogens. These results suggest that the amorphous phase appears when the size of the Curdlan molecules is larger than the average intermolecular distance, resulting from the random coil to triple helix transformation of Curdlan molecules associated with lowering hydroxide anion concentration in the dialysis process.