A process for producing ethanol from a fibrous lignocellulosic raw material. After pre-treatment of the raw material, the fibrous fraction is first hydrolysed at high consistency and then the modified material is subjected simultaneously to continued hydrolysis with a cellulase and to ethanol fermentation in a fermentation mixture. Fermentation is continued to convert an essential portion of the available cellulose into ethanol, then a liquid fraction containing solubilized hemicelluloses is added to the fermentation mixture and fermentation continued. By means of the invention, high fermentation rates, high ethanol concentrations and low ethanol production costs can be attained.