Oxidative stress, driven by excessive reactive oxygen species, contributes to aging and numerous diseases. Hydroxyl radicals (·OH) are among the most reactive and damaging species involved in oxidative stress. This study evaluated the hydroxyl radical scavenging activity of four structurally related benzoic acid derivatives commonly found in superfoods: benzoic acid, 4-hydroxybenzoic acid, 3,4-dihydroxybenzoic acid, and gallic acid, containing 0, 1, 2, and 3 hydroxyl groups, respectively. Hydroxyl radical scavenging activity was measured using the Hydroxyl Radical Antioxidant Capacity and Hydroxyphenyl Fluorescein assays. Activity increased in the order: benzoic acid < 4-hydroxybenzoic acid < 3,4-dihydroxybenzoic acid ≈ gallic acid, demonstrating that hydroxyl group substitution enhances antioxidant capacity. These findings provide new insight into the structure–activity relationships of benzoic acid derivatives. To our knowledge, this is the first study to systematically examine the antioxidant effects of the sequential addition of three hydroxyl groups on to a benzoic acid scaffold.