•Mango seed (MS) is a valuable by-product rich in bioactive compounds and antioxidants.•Optimized UAE parameters yielded a MS extract with a gallic acid content of 1.97 mg/g.•Polyphenols profile modified in extraction method, with gallates and gallotannins predominating in MS.•DPPH and ABTS values were higher in thermal extract than optimized UAE extract.•Thermal and ultrasound extracts of MS can be used as functional ingredients. The mango seed (MS) is a by-product with a high content of bioactive compounds and antioxidant capacity (AOX). Ultrasound-assisted extraction (UAE) has been recognized as an efficient technology for the extraction of bioactive compounds in plant materials. Nonetheless, it is essential to optimize the process conditions and compared with conventional technologies. The objective of this study was to compare the profile of bioactive compounds and AOX in an optimized ultrasound extract with a thermal extract. The optimized parameters for UAE included exposure to light, 1 s ultrasound pulse, 8 min extraction, 40 % amplitude, 60 °C extraction temperature, 20 % (v/v) ethanol, 35:1 (v/w) liquid-to-solid, and 850 µm particle size and showed gallic acid content of 1.97 mg/g MS. The thermal extract had a higher total soluble phenol content, mainly composed of gallates and gallotannins. Nevertheless, specific compounds, such as maclurin galloyl glucoside and quercetin xyloside, were uniquely identified in the UAE-optimized extract. DPPH and ABTS values were higher in the thermal extract. The half-maximal inhibitory concentration for the thermal treatment was 15.93 mg, while for UAE, it was 19.77 mg GAE/mL. Both thermal and ultrasound mango seed extracts exhibit significant potential as functional ingredients due to their high content of polyphenols and AOX.