Results are presented on the hot water prehydrolysis of sugar cane bagasse for obtaining ethanol by fermentation. The experimental study consisted of the determination of the effect of temperature and time of prehydrolysis on the extraction of hemicelluloses, with the objective of selecting the best operating conditions that lead to increased yield of extraction with a low formation of inhibitors. The study, carried out in a pilot plant scale rotational digester, using a 32 experimental design at temperatures of 150-190°C and times of 60-90 min, showed that it is possible to perform the hot water prehydrolysis process between 180-190°C in times of 60-82 min, yielding concentrations of xylose ≥ 35 g/L, furfural ≤ 2.5 g/L, phenols from soluble lignin ≤ 1.5 g/L, and concentrations ≤ 3.0 g/L of hemicelluloses in the cellolignin residue. These parameters of temperature and prehydrolysis time could be used for the study of the later hydrolysis and fermentation stages of ethanol production from sugar cane bagasse.