Quinolones are synthetic and commonly used antibiotics for treatment of multiple clinical infections in the world. Quinolones are clinically important antibiotics, as an ideal component, because of high potency, broad-spectrum activity, good bioavailability and a potentially low incidence of side-effects. These antibiotics are not originated from biological source. In addition to chromosomal mutations in the target genes which confer resistance to these antibiotics, in recent years, plasmids-mediated quinolone resistance (PMQR) have made difficult to treat infections caused by resistant organisms. PMQR plays a very important role in resistance to these antibiotics due to the rapid spread between the bacteria. So far, three types of PMQR have been identified, including the aac(6')-Ib-cr, the qepA efflux pump and the qnr proteins. In this research, the role of qnr proteins in the development of drug resistance to the quinolone compounds has been studied.