Corncobs are rich in hemicellulose, which has very important applications in the food industry and biofuels. In this study, hemicellulose was extracted from corncobs after a delignification pretreatment using a three-step extraction. The yield of hemicellulose was nearly 77.64% of the total available hemicellulosic polysaccharides in the pretreated corncobs. Three corresponding fractions H_W, H_A and H_E were obtained, and they all exhibited narrow polydispersity. The amount of H_A extracted by alkali accounted for 86.86% of the total amount of the isolated hemicellulose. Its average molecular mass was 24 322 g mol⁻¹, which was much higher than that of H_W (2497 g mol⁻¹) and H_E (2680 g mol⁻¹). H_W had a higher thermal stability than the other two fractions and structural analysis indicated that the main structures of these three fractions were slightly different. Nuclear magnetic resonance indicated that fraction H_A was mainly composed of 4-O-methyl-α-D-glucurono-α-L-arabino-β-D-xylan. Structural characterization of the hemicelluloses extracted using the three extraction steps will provide information for their further applications in food, pharmaceuticals and other industrial fields.