Abstract: Preextraction of hemicellulose from corn stover under microwave irradiation was studied in this paper. The experimental results indicated that the extraction yield of hemicellulose was increased by 10% to 30% under microwave irradiation in 20 min, comparing to that without microwave irradiation in 2 h even 20 h.The effect of liquidtosolid ratio (V(water)∶m(stover)), alkali consumption (m(NaOH)∶m(stover)), time, microwave power, and temperature on the extraction yield of hemicellulose was also investigated. The optimal processing parameters were: liquidtosolid ratio of 20, alkali consumption of 1.5, time of 20 min, microwave power of 1 167 W, and the particle size of 40 mesh per square inch. The obtained hemicellulose was qualitatively analyzed by IR spectroscopy, and the mechanism of microwavealkali process was also discussed.