A proposal of adsorption mechanism that explains a multilayer character of the adsorption itself as well as shapes of adsorption isotherms is presented. Changes in the before-mentioned mechanism due to exposure to magnetic field are also explained. Study revealed that in most cases presence of magnetic field decreases an amount of PEI adsorbed and this decrease is not a linear function of magnetic field strength - the tendency is reversed for the strongest field investigated (what is consistent with literature data).