Na-montmotillonite (Na-MMT) was organically modified using Octadecy Trimethyl Ammonium Bromide (OTMAB) as a modifier to improve its adsorption capacity of aflatoxin B₁ (AFB₁). The modified Na-MMT is characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Scanning electron microscopy (SEM), and Thermogravimetric analysis (TGA). The results showed that the OTMAB was intercalated into the Na-MMT, expanded its interlayer spacing (d_0.01), and increased its specific surface area. The adsorption isotherm of AFB₁ on the modified Na-MMT is followed the Langmuir equation. The maximum adsorption capacity (q_max) and the Langmuir adsorption coefficient (k) of modified Na-MMT for AFB₁ were 34.25 mg/g and 3.65 L/mg, respectively, which were both larger than those of Na-MMT (i.e. q_max=28.74 mg/g, k=2.37 L/mg), indicated that the organic modification could increase the adsorption capacity of Na-MMT for AFB₁.