Smectites separated from three soils of Ganges Floodplain, Bangladesh, were characterized. The smectites content in the fine clay fractions was in a range of 62 and 88%. Expansion to 1.8 nm by the Greene-Kelly test and the (060) spacingaround 0.150 nm suggested that the smectites were mainly beidellite-type. Elemental composition calculated from total chemical analysis showed that the smectites had layer-charge of tetrahedral-origin and were rich in Fe. The structural formula for the smectites of Silty Ganges Alluvium, which is hardly subjected to decalcification, was estimated as (Si_6.90Al1.10)(Al_2.46Fe_0.99Mg0.76) O₂₀ (OH) ₄X_1.25. The impact of iron-rich beidellite on the soil fertility potential was discussed.