Objective To study the distribution of class I integron in extended spectrum β-lactamases(ESBLs)producing Escherichia coli (E.coli) and Klebsiella pneumoniae (K.pneumoniae) and investigate the mechanism of integronmediated multi-drug resistance of ESBLsproducing strains. Methods The presence of class I integron and blaTEM, blaSHV and blaCTXM genes for coding class I integron were detected by PCR among 100 ESBLsproducing E.coli and K.pneumoniae. The gene cassettes in class I integron were detected and sequenced. Results The percentage of expression of class I integron was found as 69% among ESBLsproducing strains. Comparing to those strains without class I integron expression, the strains with class I integron presented significantly higher resistance to 12 antibiotics (P<0.05), including cephalosporins, quinolones, sulfonamides and β-lactam enzyme inhibitors, etc. The expressions of class I integron were 84.4%, 72.9% and 68.9% in the stains with blaSHV, blaTEM and blaCTXM. Conclusions Prevalent distribution of class I integron in ESBLsproducing E.coli and K.pneumoniae was found. Integrons showed definite influence on the development of multidrug resistance．