A new cellulose derivative, pentyl ether of hydroxypropyl cellulose (P-HPC), and its crosslinked gel (PG-HPC) were prepared in non-aqueous solution. The temperature dependence of the optical pitch for the thermotropic mesophases formed by P-HPC and PG-HPC was determined spectroscopically. PG-HPC displayed the cholesteric reflection colour at room temperature and its cholesteric order and structure were fixed on heating up to 90 degrees C. The optical pitch of the redried gel of PG-HPC, after swelling in tetrahydrofuran (THF), was shifted to lower wavelength and the reflection band became narrower than that of the original, before swelling in THF.