A new method for selective separation of wood components is presented. Based on Hansen's theory of solubility, ionic liquid (IL) 1-butyl-3-methylimidazolium bromine ([Bmin]Br) was mixed with aqueous ethanol. HBr the acid catalyst in the degradation of wood components, was found to form in situ by ion exchange between IL and organic acid. The hydrogen bonding capacity of the mixture was enhanced as the presence of IL, which led to the promotion of the solubilization of lignin and other products from carbohydrates hydrolysis. The data showed that, variations of the IL concentration caused cellulose to be separated from pine wood with a purity of more than 94%, or to be hydrolyzed and converted into saccharides together with hemicellulose. Because of the complete hydrolysis of hemicellulose, the cross-linked matrix of lignin and hemicellulose was destroyed, which led to the isolation of lignin with a high purity of about 93%.