This study looks at nutrition and oxidative stress and innate immunity in 15 feline patients with diabetes mellitus (DM) and 20 control cats that were fed Purina DM for 8 weeks. Measurement of oxidative stress and neutrophil function were done before and after the dietary assay. Plasma superoxide dismutase (SOD) was significantly lower in DM cats compared to control cats, confirming a greater degree of oxidative stress in the former. Plasma glutathione peroxidise, an antioxidant enzyme, increased in both groups after the 8 weeks of dietary assay. Other parameters remained steady during the study and with no differences between groups. These findings support the antioxidant supplementation for cats with DM.