The oligosaccharides, present in soybeans, are considered beneficial to humans because they are used as prebiotics that promote the growth of bifidobacteria. In the soybean germination, the α-galactosidase can be activated with consequent hydrolysis of the oligosaccharides into simple sugars. The objective of this work was to evaluate the effects of the photoperiod, temperature and germination time of BRS 257 soybean on the activity of endogenous α-galactosidase and the soluble sugars content. Sanitized soybean seeds were submitted to the germination process using the experimental design 23. The investigated variables were, the photoperiod (h), temperature (°C), germination time (days), and the response functions evaluated were α-galactosidase (UA/g germinated soybean) and soluble sugars content as glucose, fructose, sucrose, raffinose, and stachyose (mg sugar per gram of germinated soybean). The endogenous α-galactosidase activity of germinated soybean was determined by spectrophotometry at 400 nm and the sugar content was quantified by high performance ion exchange liquid chromatography with pulsed amperometric detection. The activity of endogenous α-galactosidase and the glucose and fructose content of the germinated soybean were influenced only by the germination time and the increase in α-galactosidase activity was 1.5-fold, whereas the glucose and fructose content increased to 29.6 and 16-fold when compared to non-germinated soybean, respectively. The sucrose content of germinated soybean was influenced by the germination temperature and time and reduced by 2.8 times in relation to non-germinated soybean. The raffinose and stachyose content of germinated soybean was influenced only by the germination time and reduced by 11 and 9.3 times in relation to non-germinated soybean, respectively. Therefore, the germination time had an effect on the endogenous α-galactosidase activity and soluble sugars content, while the temperature influenced only the sucrose content of germinated soybean.