(NH4)(2)SO4 solution was employed to pre-treat regenerated cellulose fiber (from bamboo) using an ultrasonic method, and then the material was heat-treated at 250 degrees C. Scanning electron microscopy revealed that erosion and cracks of the fiber surface increased after being impregnated with (NH4)(2)SO4 combined with ultrasonic pretreatment. There was a small change in the intensity and the position of some peaks in the Fourier transform infrared spectra, and in the heat treatment, partial pyrolysis of the cellulose occurred. The data showed that for the cellulose fiber pretreated with 5 wt% (NH4)(2)SO4 the decomposition temperature shifted to the lower side (252 degrees C), and the decomposition range (180 degrees C to 454 degrees C) was wider than for the other impregnation fibers and reference. However, the rate of decomposition was different with different concentrations of (NH4)(2)SO4. The C content of heat-treated fiber with 5 wt% (NH4)(2)SO4 increased to 52%. The above results indicated that the (NH4)(2)SO4 was an effective catalyst to pretreat regenerated cellulose fiber in the pathway of pyrolysis.