In this study, investigations were performed on the effect of atmospheric pressure plasma modification after the retanning process on sheep leathers and wastewater of the processes. The plasma treatments of the leather samples were carried out with an argon containing corona discharge at atmospheric pressure. Argon atmospheric pressure plasma (APP) activation was applied to the crust sheep leather surface with different times (0, 3, 6, 9 sec/cm(2)). After argon APP application, the crust sheep leathers were processed by traditional retannage. The surface properties of the treated sheep leathers were characterised by scanning electron microscopy (SEM) and an atomic force microscopy (AFM). The chemical composition of the leather surfaces was evaluated by ATR-FTIR and the surface state of the leathers was determined by contact angle measurements. The discharged chrome retanning and retanning wastewaters at the end of the processes were examined in order to determine the differences in the wastewater in terms of COD, BOD5, conductivity, turbidity, pH, salinity, total dissolved solids content (TDS) and total chromium content analyses.