Development of protein delivery systems is important for biomedical applications such as immunotherapy. Ovalbumin (OVA) is a major component of egg whites, and is a possible cause of egg allergy. In this study, OVA was used as a model protein to develop a delivery system using guanidine-terminated dendrimers (Gdn-den) bearing an amyloid-promoting peptide derived from the helix B (hB) region of OVA (hB-Gdn-den). OVA nanoparticles (NPs) were prepared by heat treatment of OVA/hB-Gdn-den mixtures. The NP size and the surface charge were controlled by adjusting the ratio of hB-Gdn-den to OVA. The NPs were around 200 nm in diameter and stably dispersed, and their encapsulation efficiency for OVA was more than 80%. Although OVA NPs were also prepared using Gdn-den, the NPs aggregated readily. Complexation with hB-Gdn-den induced conformational changes in the OVA, and the hB peptide promoted digestion of OVA. These suggest that the hB peptide of the Gdn-den works as a possible anchor to OVA. The positively charged OVA NPs effectively associated with RAW264 cells. Thus, the amyloid-promoting Gdn-den, when mixed with OVA at a suitable molar ratio to form NPs, could act as a carrier for delivery of antigen proteins to immune cells.