Tanning of hides and skins to convert them into leather can have a considerable environmental impact. Wastewater treatment technology can successfully purify leather wastewater. The first part of this research investigated the influence of Al-2(SO4)(3) concentration on the velocity of tannery wastewater settling. The wastewater sample was taken from two of the most polluted wastewater flows after liming and after chrome tanning. These wastewater flows were mixed together in a ratio of 1: 1. The second part was carried out with the samples of wastewater mixed together with different concentrations of Al-2(SO4)(3). The behaviour of settling was investigated after an addition of different concentrations of anionic polyelectrolytes in these samples. The pH, suspended solids mass, volume of sediment, gamma(Na2S), gamma(Cr2O3), chemical oxygen demand, along with turbidity in the supernatant were determined in the obtained sludge. The results demonstrate the influence of Al-2(SO4)(3) and anionic polyelectrolyte concentrations on the parameters studied and the improvement of environmental properties.