The effects of pretreatments applied to raw materials and microorganism selection in lignocellulosic bioethanol production were investigated. It has been found that the yield of enzymatic pretreatment process applied after the chemical pretreatment is about 4 times higher than that only chemical. Enzymatic pretreatment used process yield is 3.5 times higher than that chemical pretreatment. When the microorganism ethanol production yield values of Saccharomyces cerevisiae and Pichia stipitis were examined, it was found that S. cerevisiae was superior to P.stipitis in chemical pretreated reactors (about 1.7 times higher) while P. stipitis' yield was higher about 1.2 times in enzymatic pretreated reactors. When the reactors which have been pretreated with both chemical and enzymatic hydrolysis and P. stipitis and S. cerevisiae used separately were examined, it was observed that there was not a great difference in terms of ethanol production yield. C. thermocellum's ethanol yield was found about 3 times lower than the S. cerevisiae and P. stipitis. According to the obtained data, it was seen that S. cerevisiae could produce ethanol with higher efficiency than P. stipitis. At the same time, the difficulty of C. thermocellum's production conditions, high energy demand and high risk of contamination, and low ethanol production yield, it is thought that it can only be used in the research phase for now. But in particular, by investigating extracellular cellulase enzyme system of C. thermocellum, genetic modifications are predicted to play an important role in the future in the second generation bioethanol production process.