Interactions between bacteria and clay minerals are ubiquitous in soil and sediments.Previous studies on bioad-sorption of bacteria focused mainly on large particles like quartz sands.Few methods for investigation of bacteria on clayey soil components are available.This study aims to establish a method for determination of adsorption of bacteria on clay minerals.Kaolinite and B.thuringiensis were used as the test bacterial strain and clay mineral.Nycodenz—density gradient solution was used to separate free bacterial cells from those adsorbed.Correlation between total protein and count of bacteria was analyzed.Suspending and separating effects of Nycodenz solution on bacteria and minerals were tested.Appropriate ranges of bacterial number and clay mineral,and equilibrium time were determined.Results show significant correlation between total bacterial protein and count of bacteria (R²=0.9919).Total protein of bacteria could be used to represent the amount of bacteria adsorbed on minerals.Data reveal that Nycodenz solution,60% (w/v) in concentration and 1.31 g ml^-1 in density,is an efficient density gradient medium to separate free bacteria from those adsorbed on clay minerals.No interferences were observed of the 12% (v/v) Nycodenz solution on protein measurement by the Bradford method.Maximum adsorption of bacteria on kaolinite occurred 60 min after getting in contact and then leveled off.The method could be extended to the study on interactions of minerals and microorganisms.