In the last decade by-products of food and beverage processing have attracted much attention due to their functionality and potential as food ingredients. Brewers’ spent grain is the major by-product of the brewing industry representing a valuable source of bioactive ingredients. The aim of this study was to assess the effect of extraction time and temperature on the efficiency of water as solvent for the extraction of bioactive compounds from brewers’ spent grain (BSG). In terms of extraction efficiency, the results from polyphenols, flavonoids and antioxidant activity, showed that the best extraction parameters for aqueous extracts are 90⁰C and 60 minutes. In comparison with the control, the best extraction method generated 87% of the phenolics and 43.46% of the flavonoids obtained by a methanol extraction. The preliminary results for the aqueous extracts showed that water can be used as extraction solvent, but a higher extraction time and temperature are needed in order to have a content in bioactive compounds similar to that of methanolic extracts. The obtained values for polyphenols, flavonoids and antioxidant activity, emphasize the importance and the opportunities of the reuse of this agro-industrial waste.