<P><B>Abstract</B></P> <P>Olive mills generate a large amount of waste that can be revaluated. This work aim to improve the production lignocellulolytic enzymes by solid-state fermentation using ultrasounds pretreated olive mill wastes. The composition of olive mill wastes (crude and exhausted olive pomace) was compared and several physicochemical characteristics were significantly different. The use of both wastes in SSF was evaluated and a screening of fungi for xylanase and cellulase production was carried out. After screening, the use of exhausted olive pomace and <I>Aspergillus niger</I> led to the highest enzyme activities, so that they were used in the study of ultrasounds pre-treatment. The results showed that the sonication led to a 3-fold increase of xylanase activity and a decrease of cellulase activity. Moreover, the liquid fraction obtained from ultrasounds treatment was used to adjust the moisture of solid and a positive effect on xylanase (3.6-fold increase) and cellulase (1.2-fold increase) production was obtained.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Ultrasounds as potential pretreatment for lignocellulosic residues. </LI> <LI> Improve cellulase and xylanase production by solid-state fermentation. </LI> <LI> Evaluation of wastes from new olive oil extraction system. </LI> <LI> Physicochemical comparison of olive mill wastes. </LI> <LI> Selection of best producers of cellulases and xylanases. </LI> </UL> </P>