A process for producing an embedded protein antigen, comprising embedding a protein antigen having two or more cysteine residues in a molecule thereof, into a hydrophobicity-imparted polysaccharid. Prior to or after the embedding of the protein antigen, the protein antigen is purified. There are provided an embedded protein antigen and a process for producing the same, which can advantageously purify the protein antigen, while suppressing the denaturation of the protein antigen as completely as possible.
