Six peptide chains different in length and sequences were synthesized by continuous flow solid phase method. Their effects on prophage induction were tested. It was found out that a pentapeptide at concentration of 25 µg/ml inhibited the spontaneous induction of prophage Lambda in E. coli strain W 3110 () and (0)RL7 s in R. Leguminosarum (lysogenic local isolate) by (99.5%) and (98.5%), respectively. This concentration was also able to inhibit the replication of the developed phages in the indicator strains. it is suggested that the peptide may block the receptor sites of the induced phages or inhibit Rec A Protease.