Abstract: A colorimetric Loop-mediated isothermal Amplification (LAMP) assay with hydroxy naphthol blue was designed for the detection of Lawsonia (L.) intracellularis which is an important pathogenic bacteria that causes animal diseases. A set of six primers was designed to target the aspartate ammonia-lyase (aspA) gene. Serial 10 fold dilutions of cultured L. intracellularis and spiked feces were used for LAMP optimization. The lower limit of the linear range of the assay in L. intracellularis was 101 L. intracellularis which is ten times more sensitive than conventional PCR. Based on testing in 210 porcine fecal samples using LAMP and conventional PCR, the agreement quotients between LAMP and conventional PCR was 0.92. These results suggest that colorimetric LAMP is a simple method for L. intracellularis detection in porcine fecal samples.