Reactive oxygen species (ROS) play a dual role in the human body; they are essential for normal cellular signaling but, when produced in excess, can disrupt metabolic processes and induce oxidative stress. The body relies on various defense mechanisms to neutralize ROS. Phenothiazine derivatives, due to their core tricyclic structure, are considered potential antioxidants. This study focused on evaluating the antioxidant capacity of perphenazine, a representative phenothiazine derivative, and comparing it to well-known antioxidants, Trolox and ascorbic acid. To achieve this, a series of spectrophotometric assays were performed: ABTS, DPPH, CUPRAC, FRAP, and superoxide anion (O2•−) scavenging. The results indicate that perphenazine shows significant antioxidant properties, particularly through its ability to reduce copper (Cu²⁺) and iron (Fe³⁺) ions and to scavenge ABTS•⁺ radicals. In contrast, its activity against DPPH• and superoxide anions was less pronounced. Relative antioxidant effectiveness, based on IC50 values, followed the order: CUPRAC > FRAP > ABTS > O2•− > DPPH. These findings suggest that perphenazine possesses selective antioxidant potential. Further studies on other phenothiazine derivatives are warranted to comprehensively assess their antioxidative potential.