A random 12-peptide library was screened against Erysipelothrix rhusiopthiae and porcine circovirus 2 recombinant Cap protein and the selected peptides were used for detecting the corresponding pathogens quickly and effectively. To our surprise， seven peptides， P1 (WHWNAP WWNGVY)， P2 (FHWTWQFPYTST)， P3 (GAMHLPWHMGTL)， P4 (HWNIWWQHHPSP)， P5 (HFFKWHTRTNDQ)， P6 (HFFRWHPSAHLG) and P7 (HFAYWWNGVRGP) with the characteristics of polystyrene plate (PS) binding target-unrelated peptides (TUPs)， were selected from the library. It has been found that P2 and P4 shared common motif of plastic binding peptide， moreover， P2， P3， P5 and P7 have been isolated repeatedly in other research groups using different targets. Then， the seven peptide phage clones were identified as the PS binding TUP phages by phage-ELISA and elution titration， particularly， P1 and P2 showed strong PS binding affinity which can not be inhibited by usual blocking buffers. In addition， all of the phages were not propagation-related TUP， but P3 showed the similar propagation rate with M13KE (vector phage). We also found that the seven PS-TUPs are rich in W， H， F， P and G， particularly， both W and H are contained in all PS-TUPs. It deduced that they may play a potential role in peptide binding to plastic. Although it is difficult to eliminate the TUP phages in phage display completely， these PS-TUPs can be used to exclude the false positive peptides rapidly and effectively and help us to obtain truly interesting peptides more accurately.