A research on influence of magnetic field of various inductions on adsorption of polyethyleneimine (PEI) onto hematite is presented. Properties of the adsorbent surface (Magnetic Force Microscopy images and nitrogen adsorption data) and its behaviour in a water solution (particle size distribution) are also studied. Moreover, new analytical approach is proposed to compare the shape of the isotherms (e.g. presence of plateaus) by calculating a reciprocal derivative. 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). (C) 2014 Elsevier B.V. All rights reserved.