Cholesteric liquid crystalline phases were observed in dimethyl sulfoxide solutions of a new chitosan derivative. This chitosan derivative had a substitution pattern which approximates that of 3,6-O-(butyl carbamate)-N-phthaloyl chitosan (BuCaPhCh). UV-visible and circular dichroic (CD) spectroscopy carried out on BuCaPhCh revealed that the cholesteric pitch is in the visible wavelength (lambda) region and is left-handed for all investigated polymer weight fraction, x, values (0.50, 0.56, 0.60, and 0.70) and solution temperatures (25-88-degrees-C). The apparent absorption maxima, lambda(a), due to selective reflection of the cholesteric phases, showed a very strong variation as x was decreased to a value near the isotropic-anisotropic solution liquid crystal transition. The change in pitch as a function of temperature (dP/dT) was negative for all of the polymer weight fractions investigated. It was determined that the pitch-temperature relationship was dissimilar in two different temperature regions : (I) infinity greater-than-or-equal-to 1 - T(c)/T greater-than-or-equal-to 1.25 and (II) 1.25 greater-than-or-equal-to 1 - T(c)/T greater-than-or-equal-to 0, where T(c) is the clearing temperature. Use of the empirical relationship (1/X(a)) - (1 - T(c)/T)nu showed that the exponent, nu, within the normalized temperature region II, varies considerably (0.05-0.22) as a function of the x value, whereas, in the normalized temperature region I, nu is almost independent of the x value. A comparison was carried out of the experimental pitch -temperature-concentration relationships determined herein relative to that expected on the basis of theoretical relationships proposed by Varichon, Ten Bosch, and Sixou (Liq. Cryst. 1991, 9, 701). It was found that there was very good agreement between theory and experiment for pitch-polymer concentration dependence. In contrast, the experimental pitch-temperature dependence showed poor agreement with that expected on the basis of theoretical predictions.