Abstract: Microcystins (MCs) are secondary metabolites produced by toxic cyanobacteria, which belong to the family of mono-cyclic heptapeptides with molecular weight about 1000Da.MCs are claimed to possess a variety of toxic effects and considered asa strong tumor inducer.Up to now, the simpler and easier MCs detection method has not been fully established.The present studyaims to establish a novel MCs detection methodology by using the principle of yeast two-hybrid system.In previous study, severalpolypeptides interacting with MCs had been identified fromthe random 12-mer peptide phage displayed library and 7-mer peptidephage displayed library.We chose three polypeptides with high affinity forMCs and cloned them into the yeast two-hybrid system.Firstly,DNA fragments encoding for those polypeptides were constructed into the yeast two hybrid expression vectors harboringActive Domain or Biding Domain, then the recombinant plasmids were co-transfected into yeast strain AH109.TheB-Gal reporter.sactivity could be easily measured by usingONPG (O-nitropheny-l B-D-galactopyranoside) as substrate and the change in B-Gal re-porter.s activity represented the presence of MCs in culturemedium,thus this paper provided amore convenient approach to de-tect MCs.