Effect of isepamicin (HAPA-B), a new aminoglycoside antibiotic, on fertility and reproductive performance in Wistar rats was studied. The drug was injected intramuscularly to rats at a daily dose of 25, 100 or 200 mg/kg. Male rats were treated for 63 days before mating and during the mating period, and female rats were treated for 2 weeks and through the mating period to the 7th day after mating. In male rats, an inhibition of body weight gain and a development of a pale color and hypertrophy of the kidney were observed in 100 and 200 mg/kg dose-groups. In female rats, inhibition of body weight gain was observed in 100 and 200 mg/kg dose-groups and a pale color of the kidney was seen in the 200 mg/kg group. No significant differences were observed in mating and fertility performance of male and female rats between the control and treated groups. Numbers of corpora lutea, implantation sites and living fetuses in the 200 mg/kg group decreased significantly. No external, visceral and skeletal anomalies due to the treatment of HAPA-B were observed in the live fetuses. No effect dose levels of HAPA-B found in this study were 25 mg/kg on parent rats and 100 mg/kg on reproduction ability and their fetuses.