Several microorganisms cause non-gonococcal urethritis (NGU). Failure to eradicate Mycoplasma genitalium from the urethra could be associated with persistent or recurrent urethritis; thus, the choice of antibiotics with activities potent enough to eradicate M. genitalium is crucial in the treatment of NGU. In in vitro studies, sitafloxacin has been shown to be highly active against Chlamydia trachomatis and M. genitalium. We treated 89 males with NGU, including 15 patients with persistent or recurrent NGU and 1 patient with post-gonococcal urethritis, with a 100-mg twice-daily dose regimen of sitafloxacin to assess its efficacy against NGU. We examined first-void urine samples for the presence of C. trachomatis, M. genitalium, Ureaplasma parvum, and Ureaplasma urealyticum. After treatment, we evaluated 73 patients for clinical outcomes and 44 for microbiological outcomes. Symptoms were alleviated in 62 (84.9%) patients, who were judged clinically cured. Microorganisms detected before treatment were eradicated in 42 (95.5%) patients, who were judged microbiologically cured. Regarding microbiological outcomes of specific microorganisms, eradication rates of C. trachomatis (n = 33), M. genitalium (n = 11), and U. urealyticum (n = 10) were 100%, 100%, and 80.0%, respectively. In all 5 patients with M. genitalium-positive persistent or recurrent NGU who had experienced treatment failures with antibiotics, the mycoplasma was eradicated. These results suggested that the sitafloxacin regimen used, which was effective on both M. genitalium and C. trachomatis infections, could be useful as an appropriate option as first- and second-line treatment of NGU.