To obtain a new oligonucleotide chemically synthesized by using a Vero toxin 1 type gene produced by enterohemorrhagic Escherichia coli(EHEC), etc., present in a specimen as a target and useful for the rapid detection, etc., of the EHEC with a high sensitivity in food poisoning and diarrhea.

This new oligonucleotide is chemically synthesized by using a nucleotide sequence encoding a gene of Vero toxin 1 type (VT1) produced by the EHEC or a Verocytotoxin-producing Escherichia coli(VTEC) present in a specimen as a target so as to be complementary to the nucleotide sequence and has base sequences represented by formulae I and II or at least 10 contiguous bases of the corresponding complementary sequence. The oligonucleotide is useful for simple and rapid detection, etc., of the EHEC or VTEC with a high sensitivity in clinical tests, especially tests on food poisoning and diarrhea. Furthermore, the oligonucoleotide is obtained by selecting a specific base sequence encoding the gene of the VT1 produced by the EHEC or VTEC and chemically synthesizing the oligonucleotide.