Abstract: The cation exchange capacity (CEC) of vermiculite concentrate is measured by ammonium chlorideethanol method. The results show that vermiculite particles must be sufficiently dispersed and wetted to make the vermiculite interlayer cations entirely exchange with NH+4 in ammonium chlorideethanol solution. The formic acid content must be deducted when NH+4 content is measured by formol titration method. To get accurate results, the titrated solution of ammonium chlorideethanol should not be heated before it is titrated with NaOH standard solution. The measured CEC of vermiculite concentrate is 60.8824×10-3 mol/100 g.