The main objective of this study was to screen endogenous microorganisms grown on olive mill solid wastes (OMSW) with the potential to ferment pentoses and produce ethanol. Two yeasts were isolated and identified as Issatchenkia orientalis, and Pichia galeiformis/manshurica. The adaptation of the strains displayed a positive impact on the fermentation process. In terms of xylose utilization and ethanol production, all strains were able to utilize xylose and produce xylitol but no ethanol was detected. Separate hydrolysis and fermentation process on hydrolysate undergo detoxification, strain I. orientalis showed the best efficiency in producing of ethanol when supplemented with glucose. Using simultaneous saccharification and fermentation process following pretreatment of OMSW, the average ethanol yield was 3 g/100 g dry OMSW. Bioethanol production from OMSW is not economic despite the raw material is cheap. (C) 2013 Elsevier Ltd. All rights reserved.