Lead (Pb) is an environmental toxicant reported to impair male reproductive system. Betaine is a natural product which has promising beneficial effects against oxidative stress. In this experimental study, we evaluated the ameliorative effect of betaine on sperm quality and oxidative stress induced by lead (Pb) in the testis of adult male mice. Sixty male Kunming mice were divided equally into four groups: control group, betaine group (1% in drinking water), lead group (100 mg kg  bw day ) and betaine + lead group. In the last group, mice were supplemented with betaine for two weeks prior to the initiation of lead treatment and concurrently during lead treatment for 3 weeks until sacrificed. Our results indicated that in the lead-administrated group, body weights together with sperm count were significantly decreased (p < .05). The numbers of abnormal sperms were found to be higher in lead-treated mice. The activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (Cat) were significantly reduced, while the level of malondialdehyde (MDA) content was increased in the testis tissue following lead treatment. The mRNA levels of antioxidant-related genes (SOD1, GPX1 and CAT) were significantly decreased in the lead group. Betaine enhanced these parameters in betaine + lead group. In testis histology span, Johnson score was decreased (p < .05) in lead group and co-treatment with betaine increased Johnson score significantly in betaine + lead group. These results indicate that betaine improves sperm quality and ameliorate oxidative damage in testis of mice exposed to lead.