OBJECTIVE: Approximately 70% of cancer patients require radiotherapy. Howev-er, despite its effectiveness in the treatment of cancer, radiotherapy can also affect and damage surrounding healthy tissues in addition to tumor-ous tissues. Since testicular tissues are highly radiosensitive, radiotherapy can cause impair -ments in spermatogenesis leading to infertility. The purpose of this study was to examine the potential radio-protective effect of dexmedetomi-dine (Dex), an alpha 2-adrenoceptor agonist, on oxi-dative stress and apoptosis in testicular tissues caused by x-irradiation in rats. MATERIALS AND METHODS: Thirty male Sprague-Dawley rats were allocated into three groups of ten (n=10): control, irradiation (IR), and IR + Dex groups. The IR group was exposed to a sin-gle dose of 2 Gy IR. The IR+Dex group was given a single intraperitoneal (i.p.) dose of 100 mu g/kg Dex before IR. The control group received a single dose of saline solution i.p. Testicular tissues removed 24 hours after IR were subjected to histochemical, bio-chemical, and immunohistochemical analysis.RESULTS: IR resulted in increased malondialde-hyde (MDA) activity and significant changes in tes-tis tissues. However, the application of Dex elevat-ed glutathione levels by preventing MDA formation. In addition, Dex decreased tubular epithelial apop-tosis via elevated Cleaved Caspase-3 expressions.CONCLUSIONS: Dex exhibited a radio-protec-tive effect against lipid peroxidation and apopto-sis caused by IR.