In recent years, irradiation treatment has emerged as a popular technique for modification of nanostructures in fabrication of high performance polymer composites. The conventional modification methods typically involve expensive chemicals, difficult processing techniques and specialized chemistry. However, the irradiation treatment is considered simple, rapid and “green” technique that operates under ambient conditions and the product is free of residual initiators and modifiers. Such modifications develop strong interfacial matrix-nanostructure interactions and exhibit notable advantages as compared to chemical approaches. High energy radiations have beneficial effects for tailoring structure and properties of nano-systems with high precision. The irradiation processes, mechanisms, strategies and composites are reviewed in this article along with the potential applications and future challenges.