Natural clinoptilolite is a natural, the shelf containing aluminum silicate non-metallic minerals that has monoclinic crystal structure symmetry, strong adsorptive, high ion exchange capacity and high speci? c surface area, have been widely used as a adsorbent.However, the hydrophilic surfaces of parent clinoptilolites are less effective in adsorbing bacteria and toxins.Chemical modification of clinoptilolites with organic cations, results in an increased hydrophobicity of the mineral surface providing a high affinity for bacteria molecules.Formic acid, an organic acidifier, has a dicky causticity and the antibacterial mechanism, which has been overused as a feed additive (acidifer) in the farming industry.The purpose of this study is to prepare formic acid-modified clinoptilolite by cation exchange and to evaluate its absorption properties on Escherichia coli O55 under ambient conditions.in vitro.Effect of clay concentration, ionic concentration, lysine concentration, and time as well as bacterial suspensions concentration on E.coli O55 adsorption was also investigated.The results show that (1)The amount of adsorption of E.coli O55 from solution to clay minerals were significantly increased with parent clinoptilolite and acid-modified clinoptilolite content increasing.(2) The adsorption processes occurring on each of the tested adsorbents reached equilibrium at 25 mg/ml clay mineral.The discrepancy may result from the different amounts of parent clinoptilolite and acid-modified clinoptilolite added, which were between 30 to 50 mg/ml clay mineral in this study.(3) Ionic strength has an importmant influence on bacteria-clay mineral interaction.The amounts of E.coli O55 adsorbed on the tested adsorbents were increased with increased concentration of NaCl and CaCl2 in medium.The data determined from the adsorption ratio showed that Ca2+ has higher influence than that Na+.(4) The adsorption processes of E.coli O55occurring on each of the tested adsorbents reached equilibrium after 2 h.Then the rate of adsorption interaction between acid-modified clinoptilolite and parent clinoptilolite decreases with time.(5) The amount of E.coli O55 adsorbed on each adsorbent decreased with increasing the concentration of lysine.(6) the amount of E.coli O55 adsorbed on absorbent agent was increased with the increasing the concentration of bacterial suspensions, and there has not saturated trendency that bacteria concentration was presented in the present study.(7) The present study showed that the desorption rate of acid-modified clinoptilolite was about 7.83%, it was much lower than parent clinoptilolite (P <0.01).(8) In addition, it was also found that there were differences from the adsorption amount of bacteria on different clay minerals.The adsorption capacity of bacteria on acid-modified clinoptilolite better than parent clinoptilolite (P < 0.01), which was attribute to the BET specific surface area and pore volume of clinoptilolite, and the weaker adsorption is mainly dominated by ion exchange and physical adsorption.The data obtained from E.coli O55 adsorption on to the tested adsorbents, and the adsorption reaction is endothermic and spontaneous.