Objectives: The aim of this study was to investigate the effect of Rebaudioside A (RebA) on acetylcholinesterase (AChE) immunoreactivity in cortical neurons of the rat brain. RebA is a steviol glycoside commonly used in the production of sweeteners. Beyond its application as a food additive for diabetes management, steviol glycosides have been shown to influence memory and learning processes. Methods: RebA was administered to rats at two concentrations (1 mg/mL and 2 mg/mL of water) over both short-term (15 days) and long-term (45 days) periods. Indirect immunohistochemical peroxidase–antiperoxidase staining was performed on histological frontal sections of the brain cortex. Results: Acetylcholinesterase-positive neurons were analyzed both morphologically and morphometrically. The results of the experiment revealed no significant morphological changes in AChE-immunopositive neurons, indicating an absence of neurotoxic effects associated with the sweetener in these neurons. However, the analysis demonstrated a reduction in AChE immunoreactivity, particularly after 45 days of treatment. Conclusions: These preliminary findings demonstrates that RebA affects the immunoreactivity of neurons positive for AChE. Given the observed effects, further studies should be implemented to investigate the exact influence of this dietary supplement on the cholinergic nervous system.