Soybean sauce,a Chinese traditional and daily condiment,is often contaminated by aflatoxin B1.An extract-free immunochromatographic assay was proposed based on fluorescent microspheres probe for the` detection of aflatoxin B1 in soybean sauce.The probe was prepared by coupling fluorescent microspheres with anti-aflatoxin B1 antibody by the 1-ethyl-3(3-dimethylaminopropyl)carbodiimides hydrochloride-mediated method.The background from the soybean sauce sample on strip was eliminated because of the optical property of the probe.The sample without extracting procedure was directly detected by diluting with 10%methanol solution.The visible detection limit for the qualitative analysis of aflatoxin B1 in the proposed method was 2.5 μg/L,which was lower than the maximum level of 5 μg/L set by the Chinese government.The results were well agreed with those obtained by liquid chromatography-mass spectrometry(LC-MS).The method showed satisfactory characteristics,such as rapid detection,easy operation,and high sensitivity,and can thus be applied for the large-scale and on-site screening of soybean sauce contaminated with aflatoxin B1.To our knowledge,this report is the first one on the qualitative detection of aflatoxin B1 in dark colored food samples directly by fluorescent microspheres probe-based immunochromatography.