A poly neutral red modified glassy carbon electrode(PNR/GCE) was prepared by electropolymerization,and characterized by cyclic voltammetry(CV).The peak current in cyclic voltammogram as an indicator was used to investigate the effects of neutral red(NR) concentration,number of scanning segments,pH value of buffer and concentration of supporting electrolyte NaNO3 on the polymerization process.Subsequently,the optimum conditions for polymerization were selected.Then a new method for the rapid detection of antimicrobial efficacy in vitro was developed with NR as an electron mediator and E-coli as a model microorganism to investigate the relationship between activity of E-coli and concentration of antibacterials.The optimum conditions for electrode modification were as follows:concentration of neutral red:0.5 mmol/L,scan segment:30,buffer:pH 7.0,supporting electrolyte:0.5 mol/L NaNO3.The highest sensitivity for the detection of antibacterials efficacy was obtained when a final absorbance value(OD600 ) for bacterial suspension of 0.5,a standard glucose-glutamic acid solution(GGA,BOD220) as nutrition and an incubating time of 40 min were selected.Under the optimum experimental conditions,the half-inhibitory concentrations of cefoperazone,amikacin,gentamycin and levofloxacin on E-coli cells were 34.15,27.98,8.83 and 11.49 mg/L,respectively.However,vancomycin,as only an antibiotic affecting gram positive bacteria,showed a poor inhibition on E-coli cells.The results obtained above were in good agreement with those obtained by classical disk diffusion method.