To achieve an optimized co-culture ratio of Scheffersomyces stipitis and Saccharomyces cerevisiae for the production of second generation bioethanol under a cell-recycle batch process. Three Sacc. cerevisiae strains were evaluated in co-culture with Sch. stipitis CBS 5773 at different ratios using synthetic medium containing glucose and xylose. Bioreactor trials indicated that the optimal condition for ethanol production using Sacc. cerevisiae EC1118 and Sch. stipitis co-culture was 1 % of O-2 concentration. To increase ethanol production with Sacc. cerevisiae/Sch. stipitis co-culture a cell-recycle batch process was evaluated. Using this process, the maximum ethanol production (9.73 g l(-1)) and ethanol yield (0.42 g g(-1)) were achieved exhibiting a tenfold increase in ethanol productivity in comparison with batch process (2.1 g l(-1) h(-1)). In these conditions a stabilization of the cells ratio Sacc. cerevisiae/Sch. stipitis (1:5) at steady state condition was obtained. Batch cells recycling fermentation is an effective process to use Sch. stipitis/Sacc. cerevisiae co-culture for second generation ethanol production.