A process for obtaining purified hemicellulose, cellulose and cellulose-hemicellulose complexes comprising the steps of adding alcohol to caustic liquor from alkali extraction of fiber to precipitate the hemicellulose and the simultaneous, or about simultaneous, density separation of hemicellulose from the caustic liquor. The alcohol transforms the soluble high molecular weight hemicellulose into a light precipitate which floats on top of the caustic liquor solution. The caustic liquor can be subjected to a second separation step whereby the insoluble components (e.g. cellulose and cellulose-hemicellulose complexes) can be removed from the caustic liquor.