A competitive lateral flow assay for the rapid detection of Salmonella choleraesuis was developed. Immuno-magnetic nanobeads were produced by covalently coupling anti-Salmonella choleraesuis antibody to magnetic nanobeads. These immuno-magnetic nanobeads were used as visually detected probes in the subsequent assay. Compared with the traditional sandwich assay, which is used for detecting macro-molecules, this new method was developed based on the competitive relationship between S. choleraesuis in the inspected sample and the outer membrane protein immobilized on the T line. Thus, only one antibody was necessary in the new assay, whereas a pair of rigorously selected antibodies were required in the sandwich assay. The sensitivity of the competitive assay for S. choleraesuis was 1.2 x 10(7) cfu/mL. In addition, no cross reactions were found in the 17 common non-Salmonella bacteria strains and in the 4 Salmonella strains of other serotypes. Thus, with satisfactory sensitivity and specificity, the assay can be applied for the rapid detection of pre-enriched culture that may contain S. choleraesuis.