A series of poly(benzophenoneimide)s(C-m-BP-PIs) having n-alkyloxymethyl side chains(-CH2O-n-CmH2m+1, m=4, 6, 8) have been examined by X-ray diffraction, differential scanning calorimetry(DSC) and polarizing optical microscopy. The samples showed basically two phase transitions and both transtion temperatures decreased with increasing side chain length. The first transitions were ascribed to glass transitions and the second ones were assigned to liquid crystal-to-isotropic transitions. Eicosane(n-C20H42) which is chemically very similar to the side chain was miscible with the side chains of C-8-BP-PI, which induced depression of the glass transition temperature.