The macroscopic order parameter S in the cholesteric liquid crystalline phase of hydroxypropyl cellulose (HPC) and ethyl cellulose (EC) solutions was calculated using refractive index data. Haller's extrapolation approach was used. The S calculated was compared with the S predicted from Doi's theory. The calculated values of S for HPC and EC solutions were in the range of 0.4–0.8 within our experimental range, and agreed with the predicted values of S obtained with Doi's theory. This result suggests that Haller's approach is valid for determining S for liquid crystalline solutions of HPC and EC, despite the scattering of the data at higher temperatures.