The chestnut industry generates large quantities of by-products, including the chestnut shell, which is a source of phenolic compounds. In this study, MIC (minimum inhibitory concentration) of chestnut shell extract was determined by the disk diffusion method. The chestnut shell was freeze-dried and milled. The extract was obtained by ultrasound assisted technique using water 70% : etanol 30% (v/v) and subsequently lyophilized. Muller-Hinton plates were inoculated with ~10⁵ CFU/mL of microorganisms. Sterile paper discs (6 mm) were placed on the inoculated culture medium and impregnated with 10 µL of each extract. Seven concentrations of extract between 0.3% and 2.1% were tested. The plates were incubated for 24h at 37ºC. The antibacterial efficacy of the extracts was indicated by a halo formed around the paper disk. The work was carried out in triplicate. Halos were found at 1.5%, 1.8% and 2.1% on Listeria monocytogenesATCC 7973 (8.32±0.06 mm for 2.1%), Enterococcus faecalis 19433 (8.94 ±0.41 mm for 2.1%), and Staphylococcus aureus ATCC (10.26±0.19 mm at 2.1%). For the remaining microorganisms no halos were observed. The tested extract showed antimicrobial activity, demonstrating potential for the control of pathogens in the food industry.