Objective: To determine the prevalence of Gardnerella vaginalis (G.vaginalis) using a nested polymerase chain reaction (PCR) method in semen from infertile men and their effects on semen quality and some inflammatory markers.Design: Prospective study.Setting:.Major medical center and medical Institute.Patients: Men with infertility (n=118).Intervention(s): None Main Outcome Measure(s): Men attending for diagnostic semen analysis as part of infertility investigations were enrolled the study.A nested PCR test was performed to confirm the infection of G.vaginalis.The relationships among the G.vaginalis infection and the semen quality and the change of some inflammatory markers were evaluated.Result(s): The overall prevalence rate for G.vaginalis in semen was 14.4%.Significantly raised levels of IL-8, but not IL-6 were found in G.vaginalis-infected patients but not in uninfected patients.The higher IL-8 levels in semen were associated with the decrease of sperm concentration, lower progressive motile sperm, higher anomalies and higher leukocytes.There was a relationship between G.vaginalis infection and lower progressive motile sperm, higher anomalies, as well as an increase in seminal leukocytes.Conclusion(s): There was a relationship between the presence of G.vaginalis in semen and alterations of some semen parameters.G.vaginalis infection can also result in the change of some inflammatory markers.