Triblock copolymers have been widely used as a material for developing drug delivery systems (DDS). In terms of architecture, triblock copolymers could be classified into symmetric and asymmetric triblock copolymers. Different types of nano-sized structures such as star micelles, flower-like micelles, and polymer vesicles could be prepared from these block copolymers, which would be very potential in delivering various types of agents such as chemical drugs, genes, and contrast agents. Additionally, the nano-sized carriers have been fabricated for environmentally sensitive (pH-sensitive or temperature sensitive) DDS or for enhancing the gene delivery efficiency. Due to their versatility in structures and drug delivery capacity, the application of triblock copolymers would definitely be expanded in near future.