Biofilm formation is a growing concern in the food industry. Escherichia coli O157:H7 is one of the most important foodborne pathogens that can persists in food and food-related environments and subsequently produce biofilms. The efficacy of bacteriophage BPECO 19 was evaluated against three E. coli O157:H7 strains in biofilms. Biofilms of the three E. coli O157:H7 strains were grown on abiotic (stainless steel, rubber, and minimum biofilm eradication concentration [MBEC ] device) and biotic (lettuce) surfaces at different temperatures. The effectiveness of bacteriophage BPECO 19 in reducing preformed biofilms on these surfaces was further evaluated by treating the surfaces with a phage suspension (10 PFU/mL) for 2 h. The results indicated that the phage treatment significantly reduced (P  < 0.05) the number of adhered cells in all the surfaces. Following phage treatment, the viability of adhered cells was reduced by ≥3 log CFU/cm , 2.4 log CFU/cm , and 3.1 log CFU/peg in biofilms grown on stainless steel, rubber, and the MBEC device, respectively. Likewise, the phage treatment reduced cell viability by ≥2 log CFU/cm in biofilms grown on lettuce. Overall, these results suggested that bacteriophages such as BPECO 19 could be effective in reducing the viability of biofilm-adhered cells.