An equation is derived which correlates the unperturbed dimensions < r2 >0 of polypeptides with the helical contents in the helix-coil transition region by using a simple model of a polypeptide chain. The model is a chain of connected balls which represent the repeating units, -CO-NH-CHR-, based on the fact that the repeating unit has a plane structure. The changing trend of the expansion factor メョ in the transition region is connected with the helical content fH. The intrinsic viscosities [ョ] of polypeptides are calculated from the unperturbed dimensions and the メョ factors. The above calculated results concerning < r2 >0 and [ョ] are compared with other authors` theoretical and experimental results. From the comparison, we concluded that our theory explains better the chain dimensional behavior of polypeptides in the helix-coil transition region than others.
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