Nucleic acids containing repetitive tandem guanines can fold into G-quadruplex (G4) motif, which are prevalent in human genome and involve in many important biological processes [1-2].Some groups have reported that the G4 structure were more stable than other nucleic acid structures in serum or living cells [3-4].These clues inspired us to explore whether nucleic acid fragments that form G4 motif is present in body fluid (such as plasma and tissue fluid) in a higher level.