Diabetes mellitus is a metabolic disorder that causes severe complications due to the increased oxidative stress induced by disease. Many plants are popularly used in the treatment of diabetes, e.g., Baccharis trimera (carqueja). The aim of this study was to explore the potential application of the B. trimera hydroethanolic extract in preventing redox stress induced by diabetes and its hypoglycemic properties. Experiments were conducted with 48 female rats, divided into 6 groups, named C (control), C600 (control + extract 600 mg/kg), C1200 (control + extract 1200 mg/kg), D (diabetic), D600 (diabetic + 600 mg/kg), and D1200 (diabetic + 1200 mg/kg). Type 1 diabetes was induced with alloxan, and the animals presented hyperglycemia and reduction in insulin and body weight. After seven days of experimentation, the nontreated diabetic group showed changes in biochemical parameters (urea, triacylglycerol, alanine aminotransferase, and aspartate aminotransferase) and increased carbonyl protein levels. Regarding the antioxidant enzymes, an increase in superoxide dismutase activity was observed but in comparison a decrease in catalase and glutathione peroxidase activity was noted which suggests that diabetic rats suffered redox stress. In addition, the mRNA of superoxide dismutase, catalase, and glutathione peroxidase enzymes were altered. Treatment of diabetic rats with B. trimera extract resulted in an improved glycemic profile and liver function, decreased oxidative damage, and altered the expression of mRNA of the antioxidants enzymes. These results together suggest that B. trimera hydroethanolic extract has a protective effect against diabetes.