In this work, a novel vaccine delivery system, biodegradable nanoparticles (NPs) in thermosensitive hydrogel, was investigated. Human basic fibroblast growth factor (bFGF)-loaded NPs (bFGF-NPs) were prepared, and then bFGF-NPs were incorporated into thermosensitive hydrogel to form bFGF-NPs in a hydrogel composite (bFGF-NPs/hydrogel). bFGF-NPs/hydrogel was an injectable sol at ambient temperature, but was converted into a non-flowing gel at body temperature. The in vitro release profile showed that bFGF could be released from bFGF-NPs or bFGF-NPs/hydrogel at an extended period, but the release rate of bFGF-NPs/hydrogel was much lower. In vivo experiments suggested that immunogenicity of bFGF improved significantly after being incorporated into the NPs/hydrogel composite, and strong humoral immunity was maintained for longer than 12 weeks. Furthermore, an in vivo protective anti-tumor immunity assay indicated that immunization with bFGF-NPs/hydrogel could induce significant suppression of the growth and metastases of tumors. Thus, the NPs/hydrogel composite may have great potential application as a novel vaccine delivery system.