Bipolar Disorder (BD) is associated with systemic toxicity, represented by changes in the biomarkers, associated with mood episodes, leading to neurological damage, which may reflect on cognitive functions and functionality, and the progression of the disease. We aimed to analyze the effect of four biomarkers superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-Px) enzymes, and thiobarbituric acid reactive substances (TBA-RS) related to oxidative stress in BD and to correlate them with cognitive functions and functionality. We studied 50 bipolar patients type I/II, in the euthymic phase, which was divided into two subgroups with 25 patients, (≤3 years and ≥10 years of diagnosis, from the first episode of mania), and 25 control patients. To analyze frontal cognitive functions and functionality, we used the tests: Frontal Assessment Battery (FAB) and Functioning Assessment Short Test (FAST), respectively. The FAST test scores results were ≤3 years (20.63±8.21), ≥10 years (27.80±12.50), and control group (9.80±5.94), p<0.001. Changes occurred in all domains. The FAB test scores were ≤3 years (14.64±2.48), ≥10 years (12.44±2.78), and control group (15.84±1.55), p<0.001, and showed lower scores in four domains. The oxidative stress showed an increase in TBA-RS levels: ≤3 years (3.18±1.17), ≥10 years (3.01±1.03) compared to the control group (1.62±0.28), p<0.0001; and in the CAT enzyme activity we found, ≤3 years (8.10±4.18), ≥10 years (9.41±4.95), compared to the control group (3.47±0.77), p<0.0001. Even during the euthymic phase, bipolar patients showed and maintained an increase in CAT activity and lipid peroxidation with significant changes in the FAB and FAST tests in different groups of patients, demonstrating impairment in cognitive functions and functionality since disease onset.