Problem The purpose of the present invention is to provide: a chiral nucleic acid adjuvant having anti-tumor activity and an anti-tumor agent. Solution The present invention relates to an adjuvant for anti-tumor agent, wherein the adjuvant comprises oligonucleotides which comprise two to four CpG motif each represented by 5-X 1 CpGX 2 -3 and has a length of 14 to 32 nucleotides, wherein a nucleic acid at 3 end side of at least two CpG motifs is connected by phosphorothioate linkage, wherein each nucleic acid at 3 end and 5 end of the oligonucleotide is S type nucleic acid connected by phosphorothioate linkage, and wherein the oligonucleotide comprises at least one nucleic acid without phosphorothioate modification. The present invention relates to an anti-tumor agent containing its adjuvant.
