In the paper, the part of investigation results of sludge conditioning influence on the rheological parameters was presented. The correlation with dewatering parameters of sewage sludge was also determinated. The tests were conducted on sludge from mechanical and biological wastewater treatment plant after fermentation process with average flow of Q = 57,000 m(3). Investigated sludge was conditioned with polyelectrolyte. To determination of the rheological curves and the liquid limits the rheometer RC 20 was used. The tests were conducted for shear velocity of 0 divided by 400/s and the measurement time of 120 s. The dose of polyclectrolyte may cause the increase of shear stress in comparison to unprepared sludge. In the paper the dependencies determining sludge dewatering degree and liquid limit (one of the rheological parameters which is not often tested in the wastewater treatment plants) were noticed. To-date results indicate that there are some dependencies between rheological parameters and dewaterability of tested sludge. Rheological properties may be useful as the control parameter in sludge treatment.