Two extraction approaches were compared, ultrasound-assisted extraction (UAE) and conventional extraction (CE), for the recovery of natural antioxidant phenolic compounds from spent coffee grounds (SCG), which could be used as cosmetics additives or nutritional supplements. Two factorial designs were used to investigate the effect of the varied process parameters: ultrasound power (50-400 W), ethanol content in the solvent (0-50 vol%) and solid to liquid ratio (20-40 mL / g.dm) for UAE, temperature (20-70 °C) and ethanol content in the solvent (0-50 vol%) for CE. Performances of UAE and CE processes were evaluated and compared regarding total polyphenols recovery, antioxidant activity of the obtained extracts and energy consumption of the process. Polyphenols recovery efficiency was influenced mostly by ethanol content in the solvent, then ultrasound power in the case of UAE and heating temperature in the case of CE. Optimal operating conditions were identified as 400W ultrasound power, 50 vol% ethanol in the solvent and 40 mL / g.dm liquid to solid for UAE, and about 50 °C heating temperature and 50 vol% ethanol content in the solvent for CE. Under these optimal conditions for each process, more than 83% and 64% of available polyphenols in SCG were recovered with UAE and CE, respectively. Ultrasound assistance thus allowed about 33% enhancement of polyphenols recovery, while dividing by more than 2 the energy consumption. Hence, ultrasound assisted extraction process was demonstrated to be an efficient and sustainable method to recover antioxidant polyphenols from spent coffee grounds.