The purpose of the work was to determine the possibility of applying a magnetic field for the conditioning of sewage sludge previously prepared by a dual chemical method. The sludge were conditioning with using PIX 113 iron coagulant and Superfloc C - 494 weak cationic polyelectrolyte. To determine the effect of the magnetic field on the parameters of sediments, the tests were carried out in several combinations, differing in the way of conditioning, flow direction and rate of sample flow through the solenoid. To determine the changes of susceptibility to dewatering, the capillary suction time test and specific resistance to filtration were used.. Then rheological properties were analyzed: flow curves and the Ostwald model. The last element of the research was to determine the quality of lechates. For this purpose, the content of ammonium nitrogen and total organic carbon was used. The results shows, that the influence of the magnetic field on sludge susceptibility to dewatering and their rheological parameters is variable, depending on factors such as the direction and speed of the flow through the coil. The sludge subjected to exposure to the magnetic field in the N-S direction, at the flow rate of 1.0 dm3/min were characterized by lowest values of the specific resistance to filtration and the capillary suction time. Analysis of rheological properties has shown that the samples conditioned in this way are characterized by the smallest values of tangential stresses and the highest viscosity. The sludge exposure to the magnetic field influenced the reduction of impurities in the lechates.