Ofloxacin presents an ample spectrum of antimicrobial action, including combating Mycobacterium leprae, and is currently employed as a substitute when the use of rifampicin is impossible. The objective of this work was to study alterations in testicular cell nuclei of suckling rats, whose dams were submitted to oral application of ofloxacin, and respective control groups. The method utilized was morphometry by the karyometric technique. The main structures observed in histological preparations of the testicles were interstitial cells, spermatogonias, and sustentacular cells. 10 Wistar rats were utilized, four treated and five controls, in the period of the first 25 days of life, whose dams received ofloxacin 12 mg/ Kg of body weight / day orally, before being killed on the 25th day after birth. The karyometric study of interstitial cells and spermatogonias revealed that there were no changes in the form of their nuclei (p > 0.05). Since sustentacular cell nuclei presented increased major diameter, minor diameter, mean geometric diameter, volume, area, volume/area ratio and perimeter, as well as an augmented and statistically different eccentricity (p < 0.05) in suckling pups whose dams were administered ofloxacin, the nuclei presented larger size and more elongated form. It was concluded that the sustentacular cells were more sensitive to the ofloxacin effect at the administered dose