Chlorophyll was dissolved in various concentrations in organic solvents, and from the rate of flow of solutions in a viscometer, the intrinsic viscosities were measured. The values were found to vary widely according to the solvent used and the concentration of chlorophyll. The values obtained for the intrinsic viscosities under different conditions fell in two separate ranges, 2.5–3.2 and 16–22, indicating that the phytol group in the chlorophyll molecule does not have rigid structure but fluctuates between two configurations according to the conditions. Situations were entirely different in the case of dilute solutions in methanol and α-picoline, in which case the intrinsic viscosity ran up to such an abnormally high level that it could not be accounted for by any possible configuration of single chlorophyll molecules. Also the absorption spectrum of chlorophyll was measured in methanol and α-picoline at various concentrations in an attempt to detect whether the anomalous viscosity is accompanied by a change in the optical property which may have a correlation to the state of the molecule in solution.