A direct contribution towards destructive, proliferative synovitis in rheumatoid arthritis (RA) has been attributed to reactive oxygen species action. Some nutrients are considered to be capable of improving the oxidant/antioxidant status in RA; however the impact of diet composition on the antioxidant capacity of serum has not yet been studied in this disease. The aim of the study was to assess the relationship between diet quality and antioxidant status in patients with RA and healthy controls. Nutritional assessment was performed, and antioxidant status in serum, without and with deproteinization (TAS and DSAS, resp.), was determined in 82 RA and 87 healthy subjects. The diet of the RA group was low-energy and imbalanced. TAS and DSAS were significantly lower in RA patients than in controls. Antioxidant status significantly correlated with the supply of foods and nutrients influencing antioxidant and anti-inflammatory defense in RA; however, in this group, TAS was more sensitive to diet than DSAS. In healthy subjects, the nonprotein pool of serum antioxidants was more tightly linked to diet. These outcomes indicate the need to monitor diet quality of patients with RA and the usefulness of TAS measurements in this monitoring.