<P><B>Abstract</B></P> <P>Among pretreatments existing to overcome the recalcitrance of the lignocellulosic biomass, imidazolium-based ionic liquids (ILs) are gaining interest to make cellulose more accessible to hydrolytic enzymes and generate fermentable sugars that are finally converted into ethanol by microbial fermentation. However, these pretreatments are usually implemented at a temperature between 80 °C and 160 °C raising realistically an energy demand problem. Here, we present an eco-friendly pretreatment strategy using the 1-ethyl-3-methylimidazolium acetate [Emim][OAc] IL at 45 °C. This energy efficient method was studied on three substrates: a model cellulose and two industrial forest residues, spruce and oak sawdusts. The viscosity of the three samples in [Emim][OAc] were followed depending on the temperature. The structures of the pretreated substrates were analyzed by scanning electron microscopy and by Fourier transform infrared spectra. Then the pretreated samples were submitted to enzymatic hydrolysis catalyzed by cellulases from <I>Trichoderma reesei</I> and to ethanolic fermentation by the yeast <I>Saccharomyces cerevisiae</I>. The ethanolic yields obtained from (ligno)cellulosic substrates were 2.6–3.9 times higher after the soft pretreatment with [Emim][OAc]. Thus, [Emim][OAc]-pretreatment at low temperature is a promising gentle method for LCB valorization into biofuels.</P> <P><B>Highlights</B></P> <P> <UL> <LI> [Emim][OAc]-pretreatment at 45 °C was assayed on 3 (ligno)cellulosic substrates. </LI> <LI> The soft IL-pretreatment disorganized the lignocellulosic architectures. </LI> <LI> Cellulases accessibility increased and enzymatic hydrolysis yields improved. </LI> <LI> Ethanolic yields were 2.6–3.9 higher after the [Emim][OAc]-pretreatment at 45 °C. </LI> <LI> This low energy demand IL-pretreatment is efficient on softwood and harwood. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>