Vaccination is credited as a significant medical achievement contributing to the decline in morbidity and mortality of infectious diseases. Traditional vaccines composed of inactivated and live-attenuated whole pathogens confer the induction of potent and long-term immune responses; however, traditional vaccines pose a high risk of eliciting autoimmune and allergic responses as well as inflammations. New modern vaccines, such as subunit vaccines, employ minimum pathogenic components (such as carbohydrates, proteins, or peptides), overcome the drawbacks of traditional vaccines and stimulate effective immunity against infections. However, the low immunogenicity of subunit vaccines requires effective immune stimulants (adjuvants), which are an indispensable factor in vaccine development. Although there are several approved adjuvants in human vaccines, the challenges of matching and designing appropriate adjuvants for specific vaccines, along with managing the side effects and toxicity of existing adjuvants in humans, are driving the development of new adjuvants. Self-assembling peptides are a promising biomaterial rapidly emerging in the fields of biomedicine, vaccination and material science. Here, peptides self-assemble into ordered supramolecular structures, forming different building blocks in nanoparticle size, including fibrils, tapes, nanotubes, micelles, hydrogels or nanocages, with great biostability, biocompatibility, low toxicity and effectiveness at controlled release. Self-assembling peptides are effective immunostimulatory agents used in vaccine development to enhance and prolong immune responses. This review describes the predominant structures of self-assembling peptides and summarises their recent applications as vaccine adjuvants. Challenges and future perspectives on self-assembled peptides as vaccine adjuvants are also highlighted.