The phage rz/rz1 gene is a membrane subunit that is required for phage lysis to breach the bacterial host's outer membrane. Because of their proclivity to excise and infect multiple hosts, they are key drivers of horizontal gene transfer resulting in the bacteria becoming a STEC. This study aim to looked at the rz/rz1 gene of E. coli strain STEC and Shigella sonnei carrying stx gene, yielded eight lytic bacteriophages, using PCR, DNA sequencing and NCBI Blast, Expasy translation and Expasy protparam for analyze. The rz/rz1 gene sequences were found to have 97.73 % to 98.90 % identical similarities with E. coli strain STEC and Shigella sonnei. According to the Kruskal-Wallis statistical test, there was a significant difference in rz/rz1 amino acid between Phage, E. coli strain STEC and Shigella sonnei (p < 0.001). The conclusion is the rz/rz1 gene of lytic bacteriophage was involved in the spread of stx gene, with significant difference of amino acid.