The aim of this study was to evaluate the plasma coenzyme Q(10) (CoQ(10)) concentration, a vitamin-like substance found in every cell, which is also viewed as the most effective membrane antioxidant, of thalassemic patients and investigate the effect of chelating agents and ferritin levels on its concentration in patients with β-thalassemia major (β-TM). The study included 44 β-TM patients undergoing deferasirox (DFRA) or deferoxamine (DFO) chelation monotherapies or combined therapy with deferiprone (L1) and DFO, 20 patients with β-thalassemia (β-thal) traits and a control group of 22 healthy sex- and age-matched subjects. Complete blood counts, liver and renal function tests, lipid profiles, ferritin and plasma CoQ(10) [by high performance liquid chromatography (HPLC)] were analyzed. The mean age (14.7 ± 7.3 years; median 14.3 years) and sex (26 males, 18 females) of the β-TM patients were not statistically different from the β-thal trait patients and the control group. The plasma CoQ(10) concentration was 0.425 ± 0.136 μmol/L in β-TM patients, 0.508 ± 0.159 μmol/L in the β-thal trait patients and 0.534 ± 0.133 μmol/L in the control group. The difference was significant in both the β-TM (p < 0.001) and β-thal trait patients (p <0.05) compared to the control group. The CoQ(10) concentration was also associated with ferritin levels in β-TM patients; the β-TM patients with high ferritin levels had a lower CoQ(10) (p <0.05) concentration. Also, higher plasma CoQ(10) levels were detected in β-TM patients undergoing DFRA treatment, according to combined therapy administered (0.457 ± 0.115 vs. 0.382 ± 0.127 mg/dL respectively, p <0.05). In conclusion, both the β-thal trait and β-TM patients have lower antioxidant capacity as demonstrated by the lower CoQ(10) levels. The type of chelating agents and ferritin levels are factors effecting CoQ(10) concentration in β-TM patients.