Cisplatin (CDDP) is widely used for treating solid cancers; however, it induces nephrotoxicity caused by oxidative stress. Here, we investigated whether radon inhalation has different effects against CDDP-induced renal injury in two mouse strains differing in radiosensitivity, and determined the appropriate dose of CDDP combined with radon inhalation for highly radiosensitive mice. CDDP was administered at 20 mg/kg weight to C57BL/6J and BALB/c mice after radon inhalation at 1000 Bq/m(3) and 2000 Bq/m(3) for 24 h. Radon inhalation had a slight positive effect against CDDP toxicity in C57BL/6J mice with respect to improved hair condition, whereas radon inhalation exacerbated CDDP-induced toxicity in BALB/c mice, such as a decrease in hair condition, higher creatinine levels, and decreased antioxidant contents (catalase and glutathione). When BALB/c mice were treated with a lower dose of CDDP (15 mg/kg) after 1000 Bq/m(3) radon inhalation, the creatinine level was reduced and the superoxide dismutase content was increased, suggesting that this combination might have a protective effect against the CDDP-induced renal damage. The supportive effect of radon inhalation shows its good potential as a candidate treatment to alleviate CDDP-induced renal damage in veterinary medicine.