Abstract The CD40 CD154 interaction is an attractive target for therapeutic intervention in various autoimmune disorders, including rheumatoid arthritis, systemic lupus erythematosus (SLE), multiple sclerosis, and myasthenia gravis. In this study, to develop a new disruption strategy of the CD40 CD154 interaction, we screened for peptides with inhibitory effects on such ligation. 2 × 10¹¹ phage display libraries displaying liner peptides of 12-mer amino acids were screened by CD40-Ig binding assay and eight phages which expressed a different respective peptide (40BP-1 to -8) were able to specifically bind to CD40. Competitive inhibition analyses showed that 3 of the 8 peptides (40BP-N1-1 APELPNMTPSWT; 40BP-N1-2 APRPHTSYSPLP; and 40BP-N1-3 GMTAPPPPRLTQ) blocked CD40 CD154 interaction when used at high concentrations. A consensus sequence (APxPPxxT) was conserved in these three peptides. These peptides may constitute a useful and novel strategy for the inhibition of the interaction between CD40 and CD154 molecules.