The present study developed a loop-mediated isothermal amplification (LAMP) assay that amplifies the fragments of O4 Salmonella enterica-specific gene rfbJ and evaluates the potential use in detection of Salmonella enterica serovar Typhimurium (ST). The detection limit of the LAMP assay was 10³ CFU/ml, which was lower than that of the PCR assay with the same target gene (10⁵ CFU/ml), confirmed by electrophoresis. The increased turbidity of the final products of LAMP was also observed with more than 10³ CFU/ml. Furthermore, the LAMP assay took only 60 min for a reaction, while the PCR assay needed 80–90 min for a reaction and approximately 30 min for the subsequent electrophoresis to confirm the specific band. The positive reaction was only observed for 55 strains of 11 serovars of O4 group Salmonella enterica. The LAMP assay developed in the present study is considered to be an effective method for specific detection of the O4 group Salmonella enterica serovars, including ST.