The aim of the study was to evaluate the occurrence of Escherichia coli producing extended-spectrum betalactamases (ESBL and/or AmpC) in the milk of cows with mastitis. A total 2,500 milk samples from mastitic cows were tested in 2014-2018. The investigations included the culture of bacteria on MacConkey agar with cefotaxime, identification with the API Rapid 32 E test, synergy disc test D68C, assessment of antimicrobial resistance by the microdilution method and confirmation of the occurrence of genes encoding ESBL and AmpC. Out of 133 isolates identified as E. coli, 87 were recognized as ESBL producers and 46 as chromosomally encoded cephalosporinase AmpC producers. The blaTEM was predominant in the ESBL producers. All 46 AmpC-positive strains had the blaCMY gene. The results confirmed the occurrence of extended-spectrum betalactamase- producing E. coli in inflammatory secretions from mastitic bovine udders. This may impact the effectiveness of treatment of mastitis and create some risk for humans.