In view of the increasing demand for essential oils from medicinal and aromatic plants, the application of irradiated polysaccharides like chitosan is a promising option. A pot experiment was performed to study the influence of various concentrations of irradiated chitosan (ICN) on growth, physiological, and yield parameters of Mentha piperita L., a plant with considerable pharmaceutical importance. The treatments were foliar spray of deionized water only (control), foliar spray of unirradiated chitosan (40 mg L-1), and ICN at 40, 80, 120, and 160 mg L-1. Among these, 80 mg L-1 ICN (treatment 4) proved to be the best for most of the parameters studied. This treatment increased the fresh and dry weights of the plant by 65.3% and 62.7%, respectively. Furthermore, 80 mg L-1 ICN also showed an increase of 22.6% and 19.7% in carbonic anhydrase and nitrate reductase activity, respectively, while chlorophyll fluorescence was increased by 16.3% compared to the control. Leaf nitrogen content showed an enrichment of 18.2% whereas phosphorus and potassium contents increased by 10.1% and 7.9%, respectively, exceeding the control. Total phenol content exhibited an increment of 18.1%. Treatment 4 (80 mg L-1 ICN) improved essential oil content and yield by 36.8% and 126.1%, respectively, at 150 days after planting (DAP). Gas chromatography revealed that menthol content increased by 14.8%; however, menthone and menthyl-acetate contents with 80 mg L-1 ICN decreased by 2.5% and 4.8%, respectively, at 150 DAP.