Rosemary (Rosmarinus officinalis) is a valuable aromatic herb native to the Mediterranean region. This study investigates the effects of foliar application of riboflavin on rosemary plants during two seasons in 2021. The first cutting season was in summer (August), and the second was in winter (December). Foliar application of riboflavin at different concentrations (25, 50, and 100 mg L^-l) increased all growth attributes at two cuts by increasing nutrients, photosynthetic pigments, and photosynthetic activity. Riboflavin at 50 mg L^–l gave the highest mean values of all the measured growth attributes at both the first and second cuts. It also increased total photosynthetic pigments by 38%. Moreover, nutritional value, essential oil production, and overall antioxidant properties were positively enhanced in riboflavin-treated plants.  Additionally, it showed the highest values of both element content and uptake. It increased oil yield (L fed^–l) by 116% and 160% at the 1st and 2nd cuts, respectively, with the highest antioxidant potential (IC₅₀ = 9.93 µl ml^–l) at the second cut. Furthermore, riboflavin at 50 mg L^–l enhanced the activities of antioxidant enzymes catalase and peroxidase. In contrast, the activities of oxidative enzymes including ascorbic acid oxidase, indole-3-acetic acid oxidase, polyphenol oxidase, and ribonuclease decreased. Furthermore, plants treated with 50 mg L^–l riboflavin increased the RNA and DNA content. These findings confirm the efficiency of the use of riboflavin at 50 mg L^–l to improve the growth of rosemary plants with high nutritional content and enhance the antioxidant activity of their essential oil.