Atrazine, a widely used herbicide in Australia, is an endocrine disruptor with the ability to cause metabolic and reproductive abnormalities in a diverse range of vertebrates. Atrazine is the most frequently detected pesticide in Victorian groundwater and there are growing concerns about its potential effects on native wildlife and human health. Previous research has primarily focused on the effects of supra-environmental atrazine levels in aquatic species and few studies have examined the potential consequences of environmentally relevant concentrations in mammals. Our study examined the effects of atrazine exposure during the peri-pubertal window in male mice. We exposed C57BL6 male mice from weaning for eight weeks to drinking water with no atrazine (n=9), low atrazine (0.5mg/kg/day, n=10), or high atrazine (5mg/kg/day, n=14). The low concentration was based on a level accepted as being safe by the NH&MRC Australian Drinking Water Guidelines. We recorded bodyweight, food and water intake throughout the study, and organ weights post mortem at 12 weeks of age. Epididymal sperm count and motility were assessed post mortem. The effects of atrazine on sperm parameters, body weight gain, food conversion efficiency and water intake were analysed by one-way ANOVA with a multiple comparison test (Tukey’s HSD) in R. Food conversion efficiency and water intake did not differ between groups (P > 0.1). Relative organ weight, sperm count and motility did not differ between groups (P > 0.1). In contrast, mice treated with the low dose of atrazine had a greater weight gain (15.10 grams ± 1.49) than the control (10.98g ± 0.72, P = 0.02) and high dose groups (11.10g ± 0.58, P = 0.01). Thus, even short-term peri-pubertal exposure to atrazine concentrations deemed safe by the NH&MRC resulted in an altered male phenotype. Further research is ongoing to determine the long-term health effects.