Oxidative Stress (OS) is considered an underlying mechanism by which dysfunctional metabolism occurs in obese subjects but there are still very few studies in canine species. The purpose of this study was to evaluate simultaneously the effects of diet on body weight, oxidative and inflammatory status in a group of 12 adult dogs. The dogs were fed a maintenance diet, integrated with natural antioxidants, for a period of 6 months. At the beginning and the end of the trial, Body Condition Score (BCS) was evaluated and haematological (CBCs, Complete Blood Counts), oxidative parameters (d-ROMs, derivatives of Reactive Oxygen Metabolites; BAP, Biological Antioxidant Potential; Retinol; α-tocopherol) and inflammatory parameters (Fibrinogen; CRP, C Reactive Protein) were performed. Significant differences (p < 0.05) emerged about BCS, hematocrit (HCT), number of platelets (PLT), d-ROMs, BAP and retinol while no differences were for α-tocopherol, fibrinogen and CRP between the two periods of different diet. In this study, dogs showed an oxidative imbalance documented by the increase in d-ROMs and the reduction of BAP and retinol. Inflammatory parameters don’t change in relation to body weight like an alteration of the oxidative status could precede the onset of inflammation. The role of oxidative stress and of integration with antioxidants should be taken into special consideration in the dietary treatment in overweight dogs