<p>Abstract: The use of melatonin (MEL) on plants has recently become widespread. Melatonin (MEL) was used as elicitor in the leaf-derived sage (Salvia officinalis L.) callus culture, which allows production in a short time regardless of environmental factors. MEL was applied to the calli in various concentrations, and the effect on the amount and quality of phytochemicals was determined. MEL stimulated the production of the maximum quantity of sage calli and the synthesis of secondary metabolites when applied as an elicitor at a certain ratio (100 M). The callus induction rate decreased while the MEL concentration increased. Among the phytochemicals scanned by HPLC and GC-MS, especially the amount of rosmaniric acid was found to increase by 75% (100 μM). The amount of rosmarinic acid decreased gradually in the 200 μM and control groups. The color differences of the callus cultures were also considerable. The color, which was quite dark brown at 100 μM MEL, turned into a light color as the amount of rosmariniric acid decreased. In addition, phytochemicals such as α-thujone (27.56%), 1.8-cineole (5.9%), camphor (16.84%) analyzed in 100 μM MEL application have the highest rates compared to other applications. Phytochemicals present in the control group but not in the MEL treatments, and components present in the treatments but not in the control were detected (1.8-cineol, some aldehyde groups). Therefore, stimulating the production of pharmacologically&nbsp;valuable phytochemicals that can be obtained with a certain amount of MEL application in sage cell culture medium will provide an important commercial advantage.</p><p><br></p>