Secondary metabolites perform diverse ecological functions in plants, providing defense against abiotic and biotic stresses and acting as a powerful antioxidant agent. The level of metabolites in each organ or tissue changes with time and the developmental stage of the plant, which determines its response to stress. However, few studies of the secondary metabolites of sugarcane, a major global crop, have been reported. This study focuses on the primary and secondary metabolites and their antioxidant activities in new and mature leaf blades of 12 sugarcane varieties. We observed that levels of primary metabolites such as amino acids, total glucose contents, and carbohydrates were higher in the young leaves than in mature leaves; in contrast, the mature sugarcane leaves showed a higher level of synthesis of secondary metabolites (such as phenolics, flavonoids, etc.) compared to that of new leaves. Interestingly, the antioxidant activities were higher in mature leaves than in new leaves. The mature leaves of Taitang172 and ROC22 possess a high total flavonoid content, and these varieties showed maximum antioxidant activities among 12 sugarcane varieties. This study provides a broad snapshot of secondary metabolites and their antioxidant activities in (new and mature leaves) different sugarcane varieties. It enhances our understanding of the metabolic localization in different leaf tissues. We speculate that exploring the metabolome through qualitative and quantitative profiling enables a more comprehensive examination of foliar metabolites.