To investigate pretreatment demand for different parts of biomass, cotton stalk was separated into stem, branch and boll shell, which were treated by liquid hot water pretreatment (LHWP) with severity from 2.77 to 4.42. Based on weight loss (WL, w/w) mainly caused by hemicellulose removal, it was found that boll shell (WL, 46.93%) was more sensitive to LHWP than stem (WL, 38.85%). Although ethanol yield of 18.3, 16.27 and 21.08 g/100 g was achieved from stem, branch and boll shell with pretreatment severity at 4.42, ratio of ethanol yield to pretreatment energy input for particular parts was different. For boll shell and branch, the maximum ratio of ethanol yield to energy input were 1.37 and 1.33 g ethanol kJ(-1) with severity at 4.34, while it was 1.20 for stem at 3.66. This indicates that different pretreatment demands for different parts of plants should be considered in order to save pretreatment energy input. (C) 2014 Elsevier Ltd. All rights reserved.