In this study it was aimed to investigate the preventive effect of commercial Bacillus subtilis strain QST 713, endophytic bacteria isolated from healthy lettuce leaves, and the effect of application time of these treatments against Pseudomonas cichorii and Pseudomonas viridiflava infections on lettuce. Bacillus subtilis strain QST 713 was applied as recommended by the manufacturer. Thirty-two endophytic bacteria were isolated and the antagonistic effect of them was investigated by the disc diffusion method in vitro. The best promising strains were selected according to the antagonistic effect against the plant pathogenic bacteria in vitro and identified as Pseudomonas gessardii and Bacillus mojavensis by MALDI-TOF MS. In vivo tests were conducted on healthy lettuce plantlets. Statistical analysis revealed that commercial Bacillus subtilis strain QST 713 was an effective treatment against both pathogens at almost all application times. Pseudomonas gessardii and Bacillus mojavensis strains prevented Pseudomonas viridiflava infection at 0 and 24h prior application and decrease the infection at all application times. Bacillus mojavensis strain was found the most effective treatment at 24h prior application against Pseudomonas cichorii infection statistically.