The goal of this study was to pretreat rice husk (RH) using a microwave-assisted pretreatment process coupled with chlorite delignification and alkaline treatment to facilitate the isolation of cellulose. The isolated cellulose was characterized and subjected to structural analysis and a thermal stability test to ascertain the efficiency of the isolation from a visual perspective. The optimum condition for the microwave-assisted pretreatment of RH was determined by response surface methodology (RSM). The effects of three independent variables—microwave power, irradiation time, and solvent ratio—were investigated based on the maximum content of the RH being pretreated. At the optimum parameters of microwave power of 400 w, a 10-min duration, and a solvent ratio of 80.0% v/v, the pretreatment efficiency of RH was 10.0%. Compared with the conventional Soxhlet technique, the microwave pretreatment was superior. The X-ray powder diffraction (PXRD) result for the isolated cellulose showed that cellulose was highly crystalline (CrI = 65.0%). Fourier transform infrared spectroscopy (FT-IR) verified that most of the lignin and hemicelluloses were removed from the isolated cellulose after the chemical treatment. Furthermore, the TGA study revealed that the thermal stability of RH cellulose was higher than the original RH.