Sequencing batch reactor (SBR) technology has been widely applied for the treatment of industrial wastewater. However, treatment applications for highly polluted wastewaters are rather limited. In this paper treatability of leather tanning wastewaters using SBR was experimentally studied. Wastewater was provided from primary settling effluent of Istanbul Leather Tanners District Treatment Plant. Wastewater COD varied between 1 050-2 900 mg L-1. SBR system was operated for 8, 12 and 24 hours cycles. COD removals up to 85% were obtained with organic loading as high as 1.45 kg COD (kg VSS.day(-1)) in 8-hour and 12-hour cycles. Settling characteristic was good, but suspended solids' concentration in the effluent was high. High loaded systems proved to be as effective as low organic loadings in terms of COD removal. Low loading systems working around 0.4 kg COD (kg VSS.day)(-1) provided 70-83 % COD removal due to inert COD production.