Potassium (K) is one of the three major nutrient elements required by plants, others being nitrogen and phosphorus. Its fixation and release in soil are important in sustainability of agronomical and ecological processes. Clays and clay mineralogical properties are also influential on soil fertility and K dynamics in soils. This work was aimed at determining relationship between exchangeable potassium concentration and soil mineralogical composition of selected soils in Limpopo Province on soil fertility for agricultural purposes. Ten soil samples were collected from three sites [Site A, Site B and Site C (the control site)] at the University of Limpopo Experimental Farm. The soil texture ranged from sandy clay loam, loamy sand and sandy loam, with most of the samples from site B classified within the sandy clay loam. Clay minerals with potassium concentrations identified among others were: K-feldspar (KAlSi3O8), mica (KAl2Si3AlO10(OH)2) and interstratified illte/smectite [KAl2(Si3Al)O10(OH)2/(Na,Ca)(Al,Mg)6 (Si4O10)3 (OH)6n(H2O)]. The values of exchangeable K concentration in the soil samples ranged from 308 meq/100g to 743 meq/100g from all sites. Based on the findings of this study, the soil texture, exchangeable K and soil mineralogical properties influence soil fertility and could be a measure of developing stable agricultural environment.