Administration of antimicrobial agent is the most frequent and significant cause of modifications to gastrointestinal bacterial microflora. The aim of the present study was to evaluate the impact on Gram-negative aerobic bacterial intestinal flora, the possible colonization of Candida spp. and the possible emergence of resistant bacterial strains in a ten rats group receiving levofloxacin at the dosage of 10mg/kg one a day for 5 consecutive days. Our result are in agreement with those of other studies and the reveal that Gram-negative aerobic bacteria are strongly suppressed during levofloxacin treatment. Neither colonization by Candida spp. nor emergence of resistant micro-organism to levofloxacin were observed. After 7 days from completing treatment, bacterial intestinal flora was restored in 8 out of 9 rats. Levofloxacin does not significantly affect intestinal microflora. Therefore, it may be suitable for selective decontamination of the gastrointestinal tract in immunocompromised patients, for prophylaxis of urinary tract infections and for treatment of intestinal bacterial infections.