Bioactive compounds extraction from underutilized beet leaves (BLs) constitutes a promising strategy to improve the sustainability of agri-food chain. In previous studies, the ultrasound-assisted aqueous extraction (with and without temperature control) of antioxidants compounds was optimized. The present study aimed to evaluate these two optimized treatments on the microbiological quality and antioxidant properties of the extracts obtained and the stability of these attributes during refrigerated storage. BLs were washed and cut into small peace (0.04cm2). Extractions were carried out: Thermosonication (TS, 90W, 1:17ratio, 16min) and Sonication (S, 90W, 1:20ratio, 16min, with ice bath). Extracts were centrifuged (10.000rpm, 10min) and the supernatant was stored for 14 days at 5°C. The microbiological quality of extracts (mesophilic aerobic bacteria (BAM), enterobacteria (EB) and molds and yeasts (M&Y)) was determined. Total polyphenols and betalains were spectrophotometrically quantified. Temperature reached by TS and S treatments were 89 and 45°C, respectively. TS caused a significant decrease (2.1log) for BAM and for EB and M&Y (counts under detection limit). Maximum polyphenols was found in TS (27.17mgGAE/gDW), probably due to the high temperature reached that favored polyphenols extraction. Betaxanthins after TS resulted lower than after S, and this is attributed to different degradation and transformation mechanisms associated with high temperatures. Betacyanins were not affected by temperature. Otherwise BAM, EB and M&Y counts from TS extracts remained below detection limit during storage. Interestingly, microbial counts in S extracts remained constant during 2 days, differently from control that showed increases from the beginning of storage. Probably sonication exerted some physical damage to microorganisms. Polyphenols presented stability for both TS and S. A decrease of 44 and 87% was observed for betalains for the TS and S, respectively, probably due to degrading enzyme inactivation during TS. Termosonication allows to obtain extracts with appropriated microbiological and antioxidant properties and stability during storage.