Licorice (Glycyrrhiza glabra L.) is a valuable plant for the treatment of several diseases. Negative effects of aluminum stress on plants have been reported and silicon may alleviate these negative effects through promoting antioxidant system. This study was conducted to investigate the effects of silicon on glycine-betaine, phytochelatin, and antioxidant parameters in licorice plant under aluminum stress. The plants were treated with silicon (0, 0.5, and 1.50 mM) and submitted to aluminum stress (100, 250, and 400 µM). Glycine-betaine contents of roots and shoots were investigated. Also, guaiacol peroxidase (GPx), peroxidase (POX), superoxide dismutase (SOD), phenylalanine ammonia lyase (PAL), 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activities, and hydrogen peroxide (H2O2) and root phytochelatin were assessed after treatment with aluminum. Results showed that aluminum stress increased the contents of glycine-betaine and root phytochelatin, activities of GPx, POX, SOD, PAL, DPPH radical scavenging, and H2O2 content (p <0.05). Application of silicon application also increased the contents of glycine-betaine, activities of GPx, POX, PAL, DPPH radical scavenging, and root phytochelatin (p <0.05) while it decreased H2O2 and SOD contents (p <0.05). Based on the findings, application of silicon is recommended for protection of licorice under aluminum stress. Manuscript profile