Abstract: Objective To study the effects of monoclonal antibody against multiple transferable resistant C （MtrC Ab） on ciprofloxacin resistance level of N.gonorrhoeae. Methods Twelve strains of N.gonorrhoeae, isolated from 1998 to 2000, were classified into resistant group and susceptible group based on their sensitivity to ciprofloxacin. MtrC Ab and NaN3 were used as inhibitors to the Mtr efflux system and added to the suspension of N.gonorrhoeae, then the quantity of ciprofloxacin uptake by and accumulation in N.gonorrhoeae was determined at 1, 5, 10, 15 and 20 minutes after the addition. Results The ciprofloxacin uptake varied between 70-120 ng and 0-80 ng in the ciprofloxacin-susceptible and -resistant group, respectively. Without inhibitors, the quantity of ciprofloxacin accumulation in the susceptible group was signifi- cantly more than that in the resistant group. After MtrC Ab or NaN3 was added, no significant changes occurred in the quantity of ciprofloxacin accumulation in either of the two groups. The Mtr efflux pump system did function in 4 strains of N.gonorrhoeae highly resistant to ciprofloxacin, but not in 6 sensitive strains or 2 strains with lower resistance. Conclusions The efflux pump system actively transfers ciprofloxacin out of the cytoplasm of N.gonorrhoeae, leading to insufficient ciprofloxacin accumulation within the bacteria, which may be an important mechanism for the resistance of N.gonorrhoeae to ciprofloxacin. MtrC Ab and NaN3 could restore the sensitivity of N.gonorrhoeae to ciprofloxacin by blocking the function of Mtr efflux pump in the bacteria.