Rosemary extract (Rosmarinus officinalis) is a natural source of bioactive compounds with significant antioxidant properties. Among these, rosmarinic acid is celebrated for its potent antioxidant, anti-inflammatory, antimicrobial, and neuroprotective properties, making it a valuable component in both traditional medicine and modern therapeutic research. Neurodegenerative diseases like Alzheimer’s and Parkinson’s are closely linked to oxidative damage, and research indicates that rosmarinic acid may help protect neurons by mitigating this harmful process. Rosmarinic acid is able to bind cupric ions (Cu2+) and interfere with the production of reactive oxygen species (ROS) produced by copper through Fenton-like reactions. This study aims to further evaluate the contribution of rosmarinic acid within rosemary extract by comparing its activity to that of isolated rosmarinic acid. By using a detailed approach that includes chemical characterization, antioxidant capacity assessment, and neuroprotective activity testing, we have determined whether the combined components in rosemary extract enhance or differ from the effects of rosmarinic acid alone. This comparison is crucial for understanding whether the full extract offers added benefits beyond those of isolated rosmarinic acid in combating oxidative stress and Aβ-induced toxicity.