Beta-lactams represent one of the most important class of antibiotics for the treatment of infectious diseases due to pathogenic bacteria. The selective pressure exerted from the wide spread use of third generation cephalosporins generated mutant beta-lactamases belonging mainly to the TEM or SHV family that are able to extend the activity spectrum of hydrolysis. Moreover, extended spectrum cephalosporins are often a good choice in clinical practice towards Enterobacteriaceae. Here we report a comparative analysis of stability between cefotaxime, desacetyl-cefotaxime and ceftazidime with some common TEM-derivatives extended spectrum beta-lactamases.