In this paper,an amplified electrochemical immunoassay using nanocomposite based labels（{dAb-ZnO-FCA}） was developed for the assay of E-coli as indicator bacteria relevant to the quality of dairy product.The {dAb-ZnO-FCA} labels were designed by exploiting nanocomposite（ZnO@SiO2） as the carriers for immobilization of detection antibody（dAb） and ferrocenecarboxylic acid（FCA）,in which dAb was used for recognition of E-coli and FCA tags served as signal-generating molecule.Greatly amplified signal was achieved in the sandwich-type immunoassay when enormous FCA linked to ZnO@SiO2.Under the optimal experimental conditions,a linear relationship between peak current of FCA and logarithmic value of E-coli concentration was obtained in the range of 2.0×102-2.0×106 cfu/mL with a detection limit（S/N=3） of 100 cfu/mL.The proposed method was used to determine E-coli in dairy product,and the recoveries of standard additions were in the range of 95.8%-105%.The results indicated that the electrochemical immunoassay gave a useful approach for E-coli analysis with rapid response,high sensitivity and specificity,and thus provided a powerful tool for estimating the quality of dairy product.