Bangladesh has been divided into 30 Agroecological Regions (AEZs) on the basis of physiography, inundation land types, soils, and agroclimate. The applied agricultural research has currently been conducted on this basis. In context of the lack of enough information on mineralogy on the AEZ basis, an attempt has been taken to study on the mineralogy of important soils from all AEZs of Bangladesh. The present experiment was carried out in order to clarify the mineralogy of soils from Region 1: Old Himalayan Piedmont Plain. Eleven soil samples consisting of eight soil series were analyzed. The clay content of the surface soils ranged from 9.1 to 18.2% and the texture was loam or silt loam by the USDA soil textural class. The 2-20 μm silt fraction was dominated by quartz, with some mica, chlorite and plagioclase, and with small amounts of K-feldspar. The <2 μm clay fraction was dominated by mica and chlorite and in most cases by the interstratified mineral of mica and chlorite. These minerals were supposed to be inherited from the parent material of metamorphic rocks. The impact of mineralogy on agriculture or land use has been discussed.