Al 2 (SO 4 ) 3 , 18H 2 O, FeCl 3 and Ca (OH) 2 were used for the treatment of tannery wastewaters. The influences of pH and coagulant dosages were studied. Conditions were optimised according to the pollutant removal efficiencies, the volume of decanted sludge and the biodegradability index improvement. The results indicate that 67-71% of total COD, 76-92% of color and 79-97% of Cr can be removed using the optimum coagulant dosages at the optimum pH range. Al 2 (SO 4 ) 3 , 18H 2 O and Ca (OH) 2 produced better results than FeCl 3 in terms of COD, color and Cr removal as well as in terms of biodegradability improvement. Moreover, Al 2 (SO 4 ) 3 , 18H 2 O and FeCl 3 produced the least amount of sludges for a given amounts of COD, color and Cr removed in comparison with Ca (OH) 2 . Al 2 (SO 4 ) 3 , 18H 2 O seems to be suitable for yielding high pollutant removals and corresponding low volumes of decanted sludges in addition to improving wastewaters biodegradability index.